#include <iostream>
#include <fstream>

using namespace std;

long n,y,sum;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool isPrime(int n)
{
    // Corner cases
    if (n <= 1)  return false;
    if (n <= 3)  return true;

    // This is checked so that we can skip
    // middle five numbers in below loop
    if (n%2 == 0 || n%3 == 0) return false;

    for (int i=5; i*i<=n; i=i+6)
        if (n%i == 0 || n%(i+2) == 0)
           return false;

    return true;
}

int main()
{
    fin>>n;

    for(y=2; y<=n; ++y) {
        if(isPrime(y)) {
            ++sum;
        }
    }

    fout<<sum;

    return 0;
}