#include<iostream>
#include<cstdio>
using namespace std;
int main()
{
	int a, b, c;
	double ans = 0.0;
	cin >> a >> b >> c;
	for (int i = 1; i <= c; i++)
		ans += 1.0/i;
	for (int i = 1; i <= a; i++)
		ans += i;
	for (int i = 1; i <= b; i++)
		ans += i*i;
	printf("%.2f\n", ans);
	return 0;
}