#include <bits/stdc++.h>

using namespace std;

ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

#define nmax 2000005

bool v[nmax];

void ciuru(int n){
    v[0] = v[1] = 1;

    for(int i = 2; i <= sqrt(n); i++){
        if(v[i] == 0){
            for(int j = 2; j <= n / i; j++){
                v[i * j] = 1;
            }
        }
    }
}

int ans;

int main()
{
    unsigned int n;
    fin >> n;

    ciuru(n);

    for(int i = 2; i <= n; i++){
        if(!v[i])
            ans++;
    }

    fout << ans;
    return 0;
}