#include <iostream>
#include <fstream>
#include <bitset>
using namespace std;

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

const int MAX_SIZE = 20000000;
bitset<MAX_SIZE + 1> markPrimeNumbers;

int main() {
    int n;
    fin >> n;
    int primeNo = 1;
    for (int i = 3; i <= n; i += 2) {
        if (markPrimeNumbers[i] != 1) {
            ++primeNo;
            for (long long j = i * 2; j <= n; j += i) {
                markPrimeNumbers[j] = 1;
            }
        }
    }
    fout << primeNo;
    return 0;
}