#include <bits/stdc++.h>
#define ll long long
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset <2000001> reached;

int getNumberOfDivisors(int n) {
    int counter = 0;
    for (int i = 2; i <= n; i++)
        if (!reached[i]) {
            counter++;
            for (int j = i * i; j <= n; j += i)
                reached[j] = 1;
        }
    
    return counter;
}


int main() {
    int n;

    fin >> n;
    fout << getNumberOfDivisors(n); 

    return 0;
}