#include <iostream>

using namespace std;

int main()
{
    unsigned N, counter = 0;;
    bool *primes;

    cin >> N;

    primes = new bool [N];

    for(unsigned i = 2; i <= N; ++i)
        primes[i] = 1;

    for(unsigned i = 2; i <= N; ++i)
    {
        if(primes[i])
        {
            for(unsigned j = i * i; j <= N; j += i)
                primes[j] = 0;
            ++counter;
        }
    }
    cout << counter;
    delete[] primes;
    return 0;
}