题解

#include<bits/stdc++.h>
using namespace std;
int main() {
    int n;
    cin >> n;
    double ans = 0;
    for (int i = 1; i <= n; i++) {
        double s=i*(i+1)/2.0;
        ans+=1/s;
    }
    printf("%.2lf",ans);
    return 0;
}