#include <cstdio>
#include <iostream>
using namespace std;

int n, s;
double f[1005][1005];

int main()
{
	cin >> n >> s;
	f[n][s] = 0;
	for(int i = n; i >= 0; --i)
		for(int j = s; j >= 0; --j)
			if(i != n || j != s)
				f[i][j] = 1.0 * ((n - i) * (s - j) * f[i + 1
 
][j + 1] + (n - i) * j * f[i + 1][j] + i * (s - j) * f[i][j + 1] + n * s) / (n * s - i * j );
	printf( "%.4f\n", f[0][0] );
	return 0;
}