#include <fstream>

using namespace std;

int n, cnt=0;
char prim[2000005];

int main()
{
    int i, j;
    
    ifstream fin;
	ofstream fout;
	fin.open("ciur.in");
	fout.open("ciur.out");
    fin>>n;
    for (i = 2; i <= n; i++)
        prim[i] = 1;
    for (i = 2; i <= n; i++)
        if (prim[i])
        {
            cnt++;
            for (j = i+i; j <= n; j += i)
                prim[j] = 0;
        }

    fout<<cnt;
	fout.close ();
	fin.close();

    return 0;
}