#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <queue>
using namespace std;
#define REP(i,n) for (int i=0;i<(n);++i)
#define rep(i,a,b) for(int i=a;i<(b);++i)
template<class T> inline bool chmin(T &a, T b){ if(a > b) { a = b; return true;} return false;}
template<class T> inline bool chmax(T &a, T b){ if(a < b) { a = b; return true;} return false;}
typedef long long ll;
const ll INF = 1LL << 60;
const ll MOD = 1e9 + 7;


int main() {
    cin.tie(0); ios_base::sync_with_stdio(false);

    vector<bool> is_prime(1000000,true);
    vector<int> prime(1000000,0);
    is_prime[0] = is_prime[1] = false;
    prime[0] = prime[1] = 0;
    int p = 0;
    for(int i = 2; i <= 1000000; ++i){
        if(is_prime[i]){
            ++p;
            for(int j = i*2; j <= 1000000; j += i) is_prime[j] = false;
        }
        prime[i] = p;
    }

    int N;
    while(cin >> N){
        cout << prime[N] << '\n';
    }
    return 0;
}
