#include<stdio.h>
int main(){
    int start,end;
    scanf("%d", &start);
    scanf("%d", &end);
    if(start>end){
        printf("Invalid input\n");
        return 0;
    }
    int sum = 0
    for (int i=start;i<=end;i++){
        sum=sum+i;
    }
    printf("%d/n",sum);
return 0;
}