Self powers Problem 48

The series, 11 + 22 + 33 + … + 1010 = 10405071317.

Find the last ten digits of the series, 11 + 22 + 33 + … + 10001000.

Answer:
9110846700

#include<bits/stdc++.h>using namespace std;const long long mod=10000000000;const long long digs=1e5;long long multimod(long long n,long long m){    long long a,b,c,d,ans=0;    a=n/digs;b=n%digs;    c=m/digs;d=m%digs;    ans=(ans+(((a*digs)%mod)*d))%mod;    ans=(ans+(((b*digs)%mod)*c))%mod;    ans=(ans+b*d)%mod;    return ans;}int main(){    long long ans=0;    for(long long i=1;i<=1000;i++)    {        long long sum=1;        long long z=i;        long long k=i;        while(z)        {            if(z%2) sum=multimod(sum,k)%mod;            k=multimod(k,k)%mod;            z/=2;        }        ans=(ans+sum)%mod;    }    cout<<ans%mod<<endl;}