A simple math program in c is giving the wrong answer. Where is the error?

Question

The following code should output: 2.000000, but it gives -0.000000. Where exactly I am getting things wrong?

#include <stdio.h>
#include <math.h>

int main(int argc, char const *argv[]) {
  // number of iterations = k.
  int k = 100;
  long double sum = 0;
  for (int n = 0; n < k; n++)
    sum += 1 / pow(2, n);
  printf("series sum = %lf", sum);

  return 0;
}