#include<bits/stdc++.h>
using namespace std;
int main(){
    double j;
    int x,y,n;
    cin>>x>>y>>n;
    j=(x+y+n)/3.0;
    printf("%.3f",j);
}

/**************************************************************
	Problem: 1957
	User: huanglingkai
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/