#include <cstdio>

long long cit() {
    long long ans = 0;
    char c = getchar();
    bool neg = false;
    while (c < '0' || c > '9') {
        if (c == '-') {
            c = getchar();
            neg = true;
            break;
        }
        c = getchar();
    }
    while (c >= '0' && c <= '9') {
        ans = (ans << 3) + (ans << 1) + (c - '0');
        c = getchar();
    }
    return (neg) ? -ans : ans;
}

void afis(long long n) {
    int l = 0;
    char c[20];
    if (n == 0) {
        putchar('0');
    }
    if (n < 0) {
        putchar('-');
        n = -n;
    }
    while (n > 0) {
        c[l++] = n % 10 + '0';
        n /= 10;
    }
    for (int i = l - 1; i >= 0; i--) {
        putchar(c[i]);
    }
    putchar('\n');
}

int main() {
    freopen("fractii.in", "r", stdin);
    freopen("fractii.out", "w", stdout);

    int n = cit();
    int fi[1000010];
    for (int i = 1; i <= n; i++) {
        fi[i] = i;
    }
    long long ans = 1;
    for (int i = 2; i <= n; i++) {
        if (fi[i] == i) {
            ans += 2 * (i - 1);
            for (int j = 2 * i; j <= n; j += i) {
                fi[j] = (fi[j] / i) * (i - 1);
            }
        } else {
            ans += 2 * fi[i];
        }
    }
    afis(ans);
    return 0;
}