#include <iostream>
using namespace std;
int f(int x, int y){
	if(x<y)
		return f(y,x);
	else if(y!=0)
		return(x+f(x,y-1));
	else
		return 0;
}

int main(){
	int x, y;
	cin>>x>>y;
	cout<<f(x,y);
	return 0;
}