#include <stdio.h>
#include <math.h>
#define _MAXN 1000000
long N;
const long PRIM[]={
2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,
73,79,83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,
179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,
283,293,307,311,313,317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,
419,421,431,433,439,443,449,457,461,463,467,479,487,491,499,503,509,521,523,541,
547,557,563,569,571,577,587,593,599,601,607,613,617,619,631,641,643,647,653,659,
661,673,677,683,691,701,709,719,727,733,739,743,751,757,761,769,773,787,797,809,
811,821,823,827,829,839,853,857,859,863,877,881,883,887,907,911,919,929,937,941,
947,953,967,971,977,983,991,997,1011};

long  valtot[_MAXN];
long  tot(int a)
{	long i;
	long q=sqrt(a);
	for(i=0; PRIM[i]<=q; i++)
	{	if(a%PRIM[i]==0)
		{	if(a/PRIM[i]%PRIM[i])
				valtot[a]=PRIM[i]*valtot[a/PRIM[i]];
			else
				valtot[a]=(PRIM[i]-1)*valtot[a/PRIM[i]];
			return valtot[a];
		}
	}
	valtot[a]=a-1;
	return valtot[a];
}

int main()
{  	long i; long long S=1;

	FILE *fin, *fout;
	fin=fopen("fractii.in", "r");
	fout=fopen("fractii.out", "w");
	fscanf(fin, "%ld", &N);
	fclose(fin);

	valtot[1]=1;
	for(i=2; i<=N; i++)
		S=S+2*tot(i);
	
	fprintf(fout, "%lld\n", S);
	fclose(fout);
	return 0;
}