#include <fstream>

using namespace std;

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

const int nMax = 2000005;

bool pr[nMax];

int sieve(int nr){
    int ans = 0;

    pr[0] = pr[1] = 1;

    for(int i = 2; i <= nr; i++)
        if(pr[i] == 0){
            for(int j = 2; i * j <= nr; j++)
                pr[i * j] = 1;
            ans++;
        }

    return ans;
}

int main()
{
    int n;

    fin >> n;

    fout << sieve(n);
    return 0;
}