#include <stdio.h>
#include <stdlib.h>

int main() {
    FILE *f;
    int i, j, n;
    double ct;
    int* v;
 

    f = fopen("fractii.in", "r");
    fscanf(f, "%d", &n);

    v = (int*)malloc(n*sizeof(int) + 1);

    ct = 1;
    for (i = 2; i <= n; i++)
        v[i] = i;

    for (i = 2; i <= n; i++) {
        if (v[i] == i) {
            for (j = i; j <= n; j += i)
                v[j] = v[j] - v[j]/i;
        }
        ct += v[i] * 2;
    }

    fclose(f);
    f = fopen("fractii.out", "w");
    fprintf(f, "%f", ct);
    fclose(f);

    return 0;
}