Simple Addition

#include<bits/stdc++.h>

using namespace std;

int arr[]= {0,1,3,6,10,15,21,28,36,45};

long long func(long long n)
{
    long long sum = 0;

    while(n)
    {
        sum += (n/10)*45 + arr[n%10];

        n/=10;
    }

    return sum;
}

int main()
{
    long long n,m,i;

    while(scanf("%lld%lld",&n,&m)==2)
    {
        if(n<0 && m<0)
            break;

        printf("%lld\n",func(m)-func(n-1));
    }

    return 0;
}