本题题解（希望法神姐也来答一下）

#include <iostream>
#include <cstdio>
using namespace std;
double e = 1, n, t;
double f(int i)
{
    double t = 1;
    for(int j = 1;j <= i;++j)
        t *= j;
    return t;
}
int main()
{
    freopen("1e9+7.in","r",stdin);
    freopen("1e9+7.out","w",stdout);
    cin >> n;
    for(int i = 1;i <= n;++i)
        e += 1 / f(i);
    printf("%.10lf", e);
    fclose(stdin);
    fclose(stdout);
    return 0;
}