C++ crash when accessing array of arrays

Question

What is the curious issue? There is no issue with i or n being out of bounds, just a crash when printing a value. Here is a minimal code example:

#include <iostream>

using namespace std;

int main()
{
    int adj[1001][1001] = {{0}};
    int D = 2;

    for (int i=1; i<6; i++)
    {
        for (int j=0; j<D; j++)
        {
            int n = 3;
            adj[i][n] = 2;
            cout << adj[0][0] << endl;
        }
    }

    return 0;
}

Compiled using LLVM CLang 3.5.0