#include<bits/stdc++.h>
using namespace std;
int main()
{int n,z,y,x;
float a;
cin>>x;
n=n/100;
z=z/10%10;                                                                                                                             
y=y%10;
a=(n+z)*1.0/(z+y); 
printf("%.2f",a);
	return 0;
}

/**************************************************************
	Problem: 1608
	User: zxh001
	Language: C
	Result: Compile Error
****************************************************************/