uva1388 Graveyard

///2014.4.12
///uva1388
///刘汝佳《算法竞赛入门经典训练指南》1.1例4

#include <iostream>
#include <cstdio>
#include <string>
#include <cmath>
#include <algorithm>
#include <climits>
using namespace std;

int main()
{
// freopen("in","r",stdin);
// freopen("out","w",stdout);
int n,m;
while( cin>>n>>m ){
double sum = 0;
for(int i=1 ; i<n ; i++){
double d1 = 1.0/n;
double d2 = 1.0/(m+n);
int num = d1*i/d2;
double a = fabs(d1*i-num*d2);
double b = fabs(d1*i-(num+1)*d2);
if(a<b)
sum += a;
else
sum += b;
}
sum *= 10000;
printf("%.4lf\n",sum );
}
return 0;
}