#include <stdio.h>

int sum(int n,int m){
	
	if(n == m){
		return n;
	}else{
		return n + sum(n+1,m);
	}
}

int main(void) {
	int a,b;
	scanf("%d,%d",&a,&b);
	
	printf("%d",sum(a,b));
	
	return 0;
}