#include <stdio.h>
#include <stdlib.h>

/* N is 1 billion */
#define N 1000000000

/* estimate the sum of 1/2 1/4 1/8 ... 1/2^N etc. */
double est() {
    double result = 0.0;
    int i;

    double denom = 2.0;
    for (i  = 1; i <= N; i++) {
        result += (1.0 / denom);
        denom *= 2.0;
    }

    return result;
}

int main() {
    double result = est();
    printf("The sum = %lf\n", result); 
    return 0;
}