#include <cstdio>

#define NMAX 507
#define KMAX 27

using namespace std;

int Num, n, m, Coord[KMAX][KMAX];
double Ans[NMAX][NMAX];

void Gauss(){
    for (int i = 1; i <= Num; ++i)
        for (int j = i + 1; j <= Num; ++j){
            double rap = Ans[j][i] / Ans[i][i];
            for (int k = 1; k <= Num + 1; ++k)
                Ans[j][k] = (double) Ans[j][k] - Ans[i][k] * rap;
        }
}

int main(){
    freopen("minesweeper.in", "r", stdin);
    freopen("minesweeper.out", "w", stdout);
    scanf("%d %d", &n, &m);
    n *= m;
    for(int i = 0; i <= n; ++i)
        for(int j = 0; i + j <= n; ++j)
            Coord[i][j] = ++Num;
    for(int i = 0; i <= n; ++i)
        for(int j = 0; i + j <= n; ++j){
            if(i == 0 && j == 0){
                Ans[Coord[i][j]][Coord[i][j]] = 1.0;
                continue;
            }
            Ans[Coord[i][j]][Coord[i][j]] = 1.0;
            if(i != 0)
                Ans[Coord[i][j]][Coord[i - 1][j + 1]] = (double) -i / n;
            if(j != 0)
                Ans[Coord[i][j]][Coord[i][j - 1]] = (double) -j / n;
            Ans[Coord[i][j]][Coord[i + 1][j]] = (double) -(n - i - j) / n;
            Ans[Coord[i][j]][Num + 1] = 1.0;
        }
    printf ("%.6lf\n", (double) Ans[Coord[n][0]][Num + 1] / Ans[Coord[n][0]][Coord[n][0]]);
    return 0;
}