#include<stdio.h>
int main()
{
    int lower_age,upper_age;
    int sum=0;
    printf("Enter the lower and upper age boundaries:");
    scanf("%d %d",&lower_age,&upper_age);
    if(lower_age<0||upper<0||lower_age>upper_age)
    {
        printf("Invalid input\n");
    }
    else
    {
        for(int age=lower;age<=upper;age++)
        {
            if(age%7==0)
            {
                sum+=age;
            }
        }
        printf("%d\n",sum);
    }
    return 0;
}