import java.util.*;
public class Main {
    public static void main(String[] args){
      	int count=0;
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
      	int m = Integer.parseInt(sc.next());
      
      	//全通りを算出
      	int totalConbination=(n+m)*(n+m-1)/2;
      	
      	//奇数となる組み合わせ=偶数+奇数の組み合わせ
      	int oddConbination=n*m;
      
      	System.out.println(totalConbination-oddConbination);
      
      
    }

}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz