#include <iostream>
#include <cstdio>

using namespace std;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int n, prim = 0;
    bool nr[2000001];
    scanf("%d", &n);
    for(int i = 2; i <= n; i++)
    {
        nr[i] = true;
    }
    for(int j = 2; j <= n; j++)
    {
        if(nr[j])
        {
            prim++;
            for(int k = 2 * j; k <= n; k += j)
            {
                nr[k] = false;
            }
        }
    }
    printf("%d\n", prim);
    return 0;

}