GCD Extreme - Euler Totient Funtion

#include <bits/stdc++.h>
using namespace std;

typedef long long ll ;
int phi[1000000+10] ;
ll S[1000000+10] ;

void pre_calculation()
{
    phi[1] = 1 ;
    for(int i=2;i<=1000000;i++)
    {
        if(phi[i]==0)
        {
            phi[i] = i-1 ;
            for(int j=i+i;j<=1000000;j+=i)
            {
                if(phi[j]==0) phi[j] = j ;
                phi[j] = phi[j] - phi[j]/i ;
            }
        }
    }
    // For each Multiple of i pairng with all its multiple and making gcd with it is
    // obiviously i so adding it to its respective multiple value
    // phi[j/i] is due for phi[j/i] will give number of values which give GCD=i
    for(int i=1;i<=1000000;i++)
    {
        for(int j=i+i;j<=1000000;j+=i)
        {
            S[j] = S[j] + (ll) (i*phi[j/i]);
        }
    }

    for(int i=1;i<=1000000;i++) S[i] = S[i] + S[i-1] ;
}

int main()
{

    pre_calculation();
    int n ;
    while(scanf("%d",&n)==1&&n!=0) printf("%lld\n",S[n]);
    return 0;
}