cdoj 邱老师看电影

//第一次写概率dp

//写成记忆化搜索的形式比递推要更方便易懂

//不过好像还是可以写成递推的形式的 但是比较那个……

#include<cstdio>
#include<iostream>
#include<cmath>
#include<algorithm>
#include<cstring>
#include<cstdlib>
#include<queue>
#include<vector>
#include<map>
#include<stack>
#include<string>

using namespace std;

int w,b;
double f[1007][1007];

double dfs(int w,int b){
    if (w==0) return 0;
    if (b==0) return 1;
    if (f[w][b]>=0) return f[w][b];
    f[w][b]=(double)w/(double)(w+b);
    if (w+b>=3){
            double tmp=((double)(b)/double(w+b))*((double)(b-1)/(double)(w+b-1));
            if (b>=3) f[w][b]=f[w][b]+(tmp*((double)(b-2)/(double)(w+b-2))*dfs(w,b-3));
            if (w>=1) f[w][b]=f[w][b]+(tmp*((double)(w)/(double)(w+b-2))*dfs(w-1,b-2));
    }
    return f[w][b];
}

int main(){
    scanf("%d%d",&w,&b);
    for (int i=0;i<=w;i++){
            for (int j=0;j<=b;j++){
                    f[i][j]=-1;
            }
    }
    printf("%.9lf
",dfs(w,b));
    return 0;
}
/*
1 3
*/