#include #define ll long long const int N = 100001; ll phi[100001], res[100001]; void solve(){ int i, j; for(i = 0; i < N; i++)phi[i] = i; for(i = 1; i < N; i++){ for(j = 2 * i; j < N; j += i){ phi[j] -= phi[i]; } } for(i = 1; i <= N; i++){ for(j = i; j <= N; j += i ) { res[j] += ( i * phi[i] ); } } } int main(){ solve(); ll n; scanf("%lld",&n); printf("%lld", (n*(res[n]+1))/2); }