#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll n;
ll max_n = 1e6+4; 
void solve(){
    ll p = 0;
    ll Prime[n];
    ll isPrime[n+1];
    for(int i=0 ; i<=n ; i++){
        isPrime[i] = true;
    }
    isPrime[0] = isPrime[1] = 0;
    for(int i=2 ; i<=n ; i++){
        if(isPrime[i]){
            p++;
            for(int j=2*i ; j<=n ; j+=i){
                isPrime[j] = false;
            }
        }
    }
    cout << p << endl;
}

int main(){
    while (cin >> n, cin.eof() != true){
        solve();
    }
    return 0;
}

