#include <fstream>
#include <vector>
#include <iostream>
using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
    int n;
    in >> n;

    int cnt = 0;
    vector<int> prim(n+1,1);

    for(int i = 2; i <= n; i++)
        if(prim[i])
        {
            cnt++;
            for(int j = i+i; j <= n; j+=i) prim[j] = 0;
        }

    out << cnt;

    return 0;
}