奶牛和轿车 Cows and Cars uva 10491

全概率公式

#include <iostream>
#include <cstring>
#include <iomanip>
 using namespace std;
  
 int main(){
 	double a,b,c;
 	while(cin>>a>>b>>c){
 		cout<<setprecision(5)<<(a*b+b*(b-1))/((a+b)*(a+b-c-1))<<'\n';
	 }
 }