import java.util.*;
 
public class Main {
	public static void main (String[] args) {
		Scanner in = new Scanner(System.in);
		
		int a = in.nextInt();
		int b = in.nextInt();
		int c = a-1;
		int d = b-1;
		
		//偶数にならない
		if(a<=1){a=0;}
		else{
		    a = ((a * c)/2);
		}
		if(b<=1){b=0;}
		else{
		     b = ((b * d)/2);
		}
		
		System.out.print(a+b);
      
	}
}
/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