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);
      
	}
} import java.util.*; util.* java 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);
      
	}
} 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);
      
	} main {
		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);
      
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) int a = in.nextInt(); a in.nextInt() in.nextInt in int b = in.nextInt(); b in.nextInt() in.nextInt in int c = a-1; c a-1 a 1 int d = b-1; d b-1 b 1 if(a<=1){a=0;}
		else{
		    a = ((a * c)/2);
		} a<=1 a 1 {a=0;} a=0 a 0 {
		    a = ((a * c)/2);
		} a = ((a * c)/2) a ((a * c)/2) (a * c) a c 2 if(b<=1){b=0;}
		else{
		     b = ((b * d)/2);
		} b<=1 b 1 {b=0;} b=0 b 0 {
		     b = ((b * d)/2);
		} b = ((b * d)/2) b ((b * d)/2) (b * d) b d 2 System.out.print(a+b) System.out.print System.out System System.out a+b a b String[] args args 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);
      
	}
} 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);
      
	}
} Main
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);
      
	}
}