#include <bits/stdc++.h>
using namespace std;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using P = pair<ll, ll>;
ll GCD(ll a, ll b) { return b?GCD(b, a%b):a; }
ll LCM(ll a, ll b) { return a/GCD(a, b)*b; }

// Eratosthenesの篩
vector<bool> primeno(1000010, true);
void Eratosthenes(int n) {
    primeno.at(0) = primeno.at(1) = false;
    int limit = sqrt(n);
    for(int i = 2; i < limit; ++i) {
        if(primeno.at(i)) {
            for(int j = 0; i*(j+2) < n; ++j) {
                primeno.at(i*(j+2)) = false;
            }
        }
    }
}

vector<int> primecnt(1000010, 0);

int main() {
    Eratosthenes(1000000);
    ll n;
    for(int i = 0; i < 1000000; ++i) {
        if(primeno.at(i)) primecnt.at(i)++;
        primecnt.at(i+1) += primecnt.at(i);
    }
    while(cin >> n) {
        cout << primecnt.at(n) << endl;
    }
}
