O.

#include <bits/stdc++.h>
using namespace std;

int main() {
    int n, m;
    cin >> n >> m;
    vector<vector<int>> dp(n + 1, vector<int> (m + 1));
    dp[1][1] = 1;
    for(int i = 1; i <= n; ++i){
        for(int j = 1; j <= m; ++j){
            if(i != 1 || j != 1)
                dp[i][j] = dp[i-1][j] + dp[i][j - 1];
        }
    }
    cout << dp[n][m];
    return 0;
}