#include <fstream>
#include <cmath>

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

unsigned long long n, i, j, nr, a[2000005];

int main()
{
    fin >> n;
    for(i=2; i<=n; i++)
        a[i] = 1;
    for(i=2; i<=n; i++)
        if(a[i])
    {
        nr++;
        for(j=2*i; j<=n; j += i)
            a[j] = 0;
    }
    fout << nr;
    fin.close();
    fout.close();
    return 0;
}