What is the reason why my code can't do 1000+ input lines?

Question

"Test: #6, time: 62 ms., memory: 228 KB, exit code: 3, checker exit code: 0, verdict: RUNTIME_ERROR
Input
1000
R621C406
ABD815
R3C24
R634C162
R695C621
R875C898
AHG626
AFE664
R95C969
R21C933
R629C648
R253C417
WQ20
AGA989
XO484
R912C396
R292C168
PI999
TR254
PH609
R207C905
R762C995
LL946
R292C805
R174C206
NY237
R345C125
R657C212
AEY185
BB81
HG448
NB654
VA829
NH784
R2C279
AR66
R555C813
R239C905
YQ299
R664C480
IU325
R691C157
R39C597
AF614
OT619
R861C285
UH114
R128C356
EU796
R875C881
R905C18
WX612
R320C311
R230C827
BH855
R228C494
R537C643
ABR841
R338C5
R795...
Output
OP621
R815C732
X3
FF634
WW695
N875
R626C891
R664C837
G95
W21
XX629
PA253
R20C615
R989C859
R484C639
OF912
FL292
R999C425
R254C538
R609C424
U207
G762
R946C324
Y292
GX174
R237C389
DU345
HD657
R185C831
R81C54
R448C215
R654C366
R829C573
R784C372
JS2
R66C44
G555
U239
R299C667
RL664
R325C255
FA691
VY39
R614C32
R619C410
JY861
R114C554
MR128
R796C151
W875
R905
R612C622
KY320
U230
R855C60
S228
XS537
R841C746
E338
HX795
R1C48
R764C310
U428
R629C534
R878C...
Checker Log
Exit code is 3"

#include <bits/stdc++.h>
#include <sstream>
using namespace std;
 
int main(){
    long long int n;
    cin >> n;
    vector<string> s;
    vector<string> results;
    map<int, string> list;
    map<string, int> l;
    l["A"] = 1;
    l["B"] = 2;
    l["C"] = 3;
    l["D"] = 4;
    l["E"] = 5;
    l["F"] = 6;
    l["G"] = 7;
    l["H"] = 8;
    l["I"] = 9;
    l["J"] = 10;
    l["K"] = 11;
    l["L"] = 12;
    l["M"] = 13;
    l["N"] = 14;
    l["O"] = 15;
    l["P"] = 16;
    l["Q"] = 17;
    l["R"] = 18;
    l["S"] = 19;
    l["T"] = 20;
    l["U"] = 21;
    l["V"] = 22;
    l["W"] = 23;
    l["X"] = 24;
    l["Y"] = 25;
    l["Z"] = 26;
 
    list[1] = "A";
    list[2] = "B";
    list[3] = "C";
    list[4] = "D";
    list[5] = "E";
    list[6] = "F";
    list[7] = "G";
    list[8] = "H";
    list[9] = "I";
    list[10] = "J";
    list[11] = "K";
    list[12] = "L";
    list[13] = "M";
    list[14] = "N";
    list[15] = "O";
    list[16] = "P";
    list[17] = "Q";
    list[18] = "R";
    list[19] = "S";
    list[20] = "T";
    list[21] = "U";
    list[22] = "V";
    list[23] = "W";
    list[24] = "X";
    list[25] = "Y";
    list[26] = "Z";
    for (int i = 0; i < n; i++){
        string coordinate;
        cin >> coordinate;
        s.push_back(coordinate);
    }
    for (string x : s){
        if (x.substr(0, 1) == "R"){
            string colresult = "";
            int b = x.find("C");
            string column = x.substr(b+1);
            stringstream geek(column);
            int col = 0;
            geek >> col;
            int quotient  = col / 26;
            int mod = col % 26;
            if (quotient == 0){
                colresult = list[mod];
            }
            else {
                colresult = list[quotient] + list[mod];
            }
            cout << colresult + x.substr(1, ((x.substr(1)).length()) - (x.substr(b).length())) << endl;
        }
        else {
            bool v = false;
            string numbers = "";
            string letters = "";
            for (int i = 0; i < x.length(); i++){
                if ((x[i] == '0' || x[i] == '1' ||x[i] == '2' || x[i] == '3' || x[i] == '4' || x[i] == '5' || x[i] == '6' || x[i] == '7' || x[i] == '8' || x[i] == '9') && v == false){
                    numbers = x.substr(i);
                    letters = x.substr(0, (x.length() - numbers.length()));
                    v = true;
 
                }
            }
            int sum = 0;
            for (int j = 0; j < letters.length(); j++){
                sum += pow(26, letters.length()-1-j) * l[letters.substr(j, 1)];
            }
            cout << "R" + numbers + "C" << sum << endl;
        }
    }
}