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

int is_prime(int n)
{
    for (int i=2; i*i<=n; i++)
    {
        if (n%i==0)
            return 0;
    }
    return 1;
}

int main()
{
    int n, cnt=0;
    FILE *fin=fopen("ciur.in", "r");
    FILE *fout=fopen("ciur.out", "w");
    fscanf(fin, "%d", &n);
    for (int i=2; i<=n; i++)
    {
        if (is_prime(i))
            cnt++;
    }
    fprintf(fout, "%d", cnt);
    return 0;
}