import java.util.*;

class Main {
  	public static void main (String[] args) throws java.lang.Exception {
		Scanner scanner = new Scanner(System.in);
		int N = scanner.nextInt();
      	int M = scanner.nextInt();
      	int nPlusMChoose2 = (N+M) * (N+M-1) / 2;
		int oddCombos = N * M;
	    int result = nPlusMChoose2 - oddCombos;
		System.out.printf("%d\n", result);
    }
}
/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