#include <bits/stdc++.h>

using namespace std;

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

int main()
{
    int n, nr = 1;
    fin>>n;
    vector <bool> a(n + 1, true);

    for(int i = 3; i<=n; i+=2){
        if(a[i] == true){
            nr++;
            for(long long j = 1ll * i * i; j<=n; j+=i)
                a[j] = false;
        }
    }
    fout<<nr;
    return 0;
}