#include <iostream>
#define DEGENERATE_BOUNDARY 2
#define NUMBER_SHED 1
#define NUMBER_LEFT 0
#define NO_REMAINDER 0
using namespace std;

const int N = 1000000 + 10;

int primeSet[N];
int primeBitMap[N];
int naturalRank;

int numberRange;

void declaration(){
    scanf("%d", &numberRange);
}

int eulerFunctions[N];
long long eulerSum;

void linearEulerCalculation(){
    eulerFunctions[1] = 1;
    for(int coefficient = DEGENERATE_BOUNDARY; coefficient <= numberRange; coefficient ++){
        if(primeBitMap[coefficient] == NUMBER_LEFT){
            primeSet[naturalRank ++] = coefficient;
            eulerFunctions[coefficient] = coefficient - 1;
        }
        for(int primeRank = 0; coefficient <= numberRange / primeSet[primeRank]; primeRank ++){
            primeBitMap[coefficient * primeSet[primeRank]] = NUMBER_SHED;
            if(coefficient % primeSet[primeRank] == NO_REMAINDER){
                eulerFunctions[coefficient * primeSet[primeRank]] = primeSet[primeRank] * eulerFunctions[coefficient];
                break;
            }
            eulerFunctions[coefficient * primeSet[primeRank]] = (primeSet[primeRank] - 1) * eulerFunctions[coefficient];
        }
    }
}

void outputResult(){
    for(int rank = 1; rank <= numberRange; rank ++){
        eulerSum += eulerFunctions[rank];
    }
    printf("%lld", eulerSum);
}
int main(){
    declaration();
    linearEulerCalculation();
    outputResult();
    return 0;
}