#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll n,rs, A[2000001];
int main(){
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");
    cin >> n;
    for(int i=2; i<=n; i++){
        int k;
        if(A[i] == 0){
            k=i;
            while(k+i <= n){
                k = k+i;
                A[k] = 1;
            }
        }
    }

    for(int i=2; i<=n; i++){
        if(A[i] == 0){
            rs++;
        }
    }
    cout << rs;
}