#include<bits/stdc++.h>
using namespace std;

typedef long long int ll;


int main()
{
	//freopen("input.txt","r",stdin);
	//freopen("output.txt","w",stdout);
	int cow,car,show,i,j,k,door;
	double pro1,pro2;
	while(cin>>cow>>car>>show)
	{
       door=cow+car;
       pro1=(cow/(double)door)*((double)(car)/(door-show-1));
       pro2=(car/(double)door)*((double)(car-1)/(door-show-1));
       double ans=pro1+pro2;
       printf("%.5lf\n",ans);
	}
	return 0;
}