#include <stdio.h>

int main()
{
    int start, end, i, sum;
    scanf("%d%d", &start, &end);
    if(start>end){
        printf("Invalid input");
        return 0;
        
    }
    for(i=start;i<=end;i++);
    sum+=i;
    }
    printf("%d", sum);
    return 0;
    }