#include <cstdio>
#include <cstring>

using namespace std;

int N, M;
long double D[2][22][22];
long double sol;

int main() {
	freopen("minesweeper.in", "r", stdin);
	freopen("minesweeper.out", "w", stdout);
	
	scanf("%d%d", &N, &M);
	N *= M;

	D[0][N][0] = 1;

	for (int i = 1; i <= 40000; i++) {
		for (int j = 0; j <= N; j++)
			for (int k = 0; k <= N - j; k++) {
					int l = N - j - k;
					if (l == N)
						continue;
					if (j > 0)
						D[1][j - 1][k + 1] += (1.0 * j) / (1.0 * N) * D[0][j][k];
					if (k > 0)
						D[1][j][k - 1] += (1.0 * k) / (1.0 * N) * D[0][j][k];
					if (l > 0)
						D[1][j + 1][k] += (1.0 * l) / (1.0 * N) * D[0][j][k];
			}

		sol += i * D[1][0][0];

		memcpy(D[0], D[1], sizeof(D[0]));
		memset(D[1], 0, sizeof(D[1]));
	}

	printf("%Lf\n", sol);


	return 0;
}