#include <fstream>
#include <string.h>
#define nmax 2000001
using namespace std;
bool v[nmax + 1];
int n;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f >> n;
    int nr = 0;
    memset(v, 1, sizeof(v));
    for (int i = 2; i <= n; i++)
        if (v[i] == 1)
        {
            nr++;
            for (int j = i * i; j <= n; j += i) v[j] = 0;
        }
    g << nr;
    return 0;
}