#include<bits/stdc++.h>
using namespace std;

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

int n,A[2000001],ans;

int main(){
    fin >> n;
    for(int i = 2; i <= n; i++)
    {
        if(!A[i])
        {
            ans++;
            int j = i + i;
            while(j <= n)
            {
                A[j] = 1;
                j += i;
            }
        }
    }

    fout << ans;
return 0;
}