#include<stdio.h>
int main()
{
    int youngest_age,oldest_age;
    int sum=0;
    scanf("%d %d",&youngest_age,&oldeest_age);
    if (youngest_age < 0||oldest_age<0||youngest_age>oldest_age)
    {
        printf("Invalid Input\n");
        return 1;
    }
    for (int i=youngest_age;i<=oldest_age;i++){
        if (i % 7==0){
            sum+=i;
        }
    }
    printf("%d\n",sum);
    return 0;
}