A7827.F的值

#include <iostream>
#include <iomanip>
using namespace std;

int n;
int fac[16] = {1};
double F = 1;

int main() {
    cout.flags(ios::fixed), cout.precision(8);
    for (int i=1; i<=15; i++) 
        fac[i] = fac[i-1]*i;
    cin >> n;
    for (int i=1; i<=n; i++) {
        if (i&1) {
            F -= 1.0/fac[i];
        }else {
            F += 1.0/fac[i];
        }
    }
    cout << F;
    return 0;
}