#include<stdio.h>
int main()
{
int a,b,c;
double s;
scanf("%d%d%d",&a,&b,&c);
s=(a+b+c)/3.0;
printf("%.3lf",s);
return 0;
}
/**************************************************************
	Problem: 1957
	User: admin
	Language: C
	Result: Accepted
	Time:9 ms
	Memory:1144 kb
****************************************************************/