#include<bits/stdc++.h>
using namespace std;
int main(){
    float a,b,c,d=0;
    cin>>a>>b>>c;
    d=(a+b+c)/3;
    printf("%.3f",d);
}
/**************************************************************
	Problem: 1957
	User: linyuhang
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/