#include<bits/stdc++.h> 
using namespace std;
int x,y,q;
float w;
int main(){
    cin>>x>>y>>q;
    w=(x+y+q)/3.0;
    printf("%.3f",w);
}
/**************************************************************
	Problem: 1957
	User: chenyichuen
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/