#include<iostream>
#include<cmath>
#include<algorithm>
#include<string>
#include<map>
using namespace std;
int main() {
    int a, b;
    double c, sum = 0;
    cin >> a >> b >> c;
    sum += (1 + a) * a / 2;
    for (int i = 1;i <= b;i++) {
        sum += i * i;
    }
    for (double i = 1;i <= c;i++) {
        sum += 1 / i;
    }
    printf("%.2lf", sum);
    return 0;
}