#include <fstream>
#define NMax 2000001
using namespace std;

bool v[NMax];
int n, i, j, s;

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

    fin >> n;

    j = 2;
    while(j <= n)
    {
        while(v[j])
            ++j;
        v[j] = 1;
        ++s;
        i = j << 1;
        while(i <= n)
        {
            v[i] = 1;
            i += j;
        }
    }

    fout << s - 1;

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