#include<iostream>
#include<cstdio>

using namespace std;

int main() {
	
	int a, b, c;
	cin >> a >> b >> c;
	
	double sum = 0;
	for (int i = 1; i <= a; i ++ ) sum += i;
	for (int i = 1; i <= b; i ++ ) sum += i * i;
	for (int i = 1; i <= c; i ++ ) sum += 1.0 / i;
	
	printf("%.2lf",sum);
	
	return 0;
}