12321

#include <iostream>
#include <math.h>
#include <conio.h>

using namespace std;

int main ()
{
    int n ,  i=0;
    double s = 0, r;

    cout <<"Input n:";
    cin >> n;
    while(i < n)
    {
        i++;
        r = 1/(pow(2,n));
        s+=r;

    }
    cout <<"Sum=" << s+1;
    getch();
    return 0;
}