#include <cstdio>
#include <vector>
#include<iostream>
#include<conio.h>
using namespace std;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int n = 10, nr = 1;scanf("%d", &n);
    vector<bool> prim(n / 2 + 1);
    for (int i = 0; i < n/2; i++)
        prim[i] = true;

    for (int i = 1; 2 * i * i + 2 * i <= n; i++)
        if (prim[i] == true)
        {
            for (int j = 2 * i * i + 2 * i; 2 * j + 1 <= n; j += 2 * i + 1)
                prim[j] = false;
        }
    for (i=1; 2 * i + 1 <= n; ++i)
        if (prim[i] == true) nr++;

    printf("%d", nr);
    return 0;
}