#include<bits/stdc++.h>
#define N 2000010

using namespace std;

int n,rs;
int a[N];

int main() {
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");

    cin>>n;

    for (int i=2; i*i<=n; i++) {
        if (!a[i])
        for (int j=i*i; j<=n; j+=i) a[j]=1;
    }

    for (int i=2; i<=n; i++) {
        rs+=!a[i];
    }
    cout<<rs;

    return 0;
}