#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
    int N;
    fin >> N;

    bool *e = new bool[N+1];
    e[0] = e[1] = false;

    for(int i=2; i<=N; i++)
        e[i] = true;

    for(int i=2; i*i<=N; i++)
        if(e[i])
            for(int j = i*i; j <= N; j+=i)
                e[j] = false;

    int Nr = 0;
    for(int i=0; i<=N; i++)
        if(e[i])
            Nr++;
    fout << Nr;

    delete e;

    fin.close();
    fout.close();
    return 0;
}