#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;
    }