#include <fstream>
#define NMAX 2000005

using namespace std;

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

int cnt, n, v[NMAX], i, j;

void ciur()
{
    for (i = 1; i <= n; i++)
        v[i] = 1;
    v[0] = v[1] = 0;
    for (i = 2; i <= n; i++){
        if (v[i] == 1)
            for (j = 2; j * i <= n; j++)
                v[j * i] = 0;
    }

}
int main()
{
    fin >> n;
    ciur();
    for (i = 1; i <= n; i++)
        if (v[i] == 1)
            cnt++;
    fout << cnt;
    return 0;
}