10491.cpp

#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
int main(){
    double ncow,ncar,nshow;
    while(scanf("%lf%lf%lf",&ncow,&ncar,&nshow)!=EOF){
                     double val1=ncar * (ncow + ncar - 1);
                     double val2=(ncow+ncar) * (ncow + ncar - nshow - 1);
                     double val=val1/val2;
                     printf("%.5lf\n",val);
    }
    return 0;
}