public int uniquePaths(int m, int n) {

final int M = Math.max(m, n) - 1, N = Math.min(m, n) - 1;

long result = 1;

for (int i = M + 1, j = 1 ; i <= M + N ; i++, j++) {

result *= i;

result /= j;

}

return (int) result;

}