#include<bits/stdc++.h>

using namespace std;
bool a[2000010];

int main(){
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    long long n , ans = 0;
    in >> n ;

    for(long long i = 2 ; i <= n ; i ++){
        if(a[i]==0){
            ans++;
            for(long long j = i * i ; j <= n ; j += i)
                a[j] = 1;

        }
    }

    out << ans ;
}