#include<bits/stdc++.h>
#define NMAX 2000010
using namespace std;

int n, rs;
bool u[NMAX];

int main() {
    ifstream cin("ciur.in"); ofstream cout("ciur.out");
    cin>>n;
    for (int i=2; i*i<=n; i++) {
        if (!u[i]) for (int j=i*i; j<=n; j+=i) u[j]=1;
    }
    for (int i=2; i<=n; i++) rs+=(!u[i]);
    cout<<rs;

    return 0;
}