#include<fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,rasp,i,j;
bool prim[2000001];
int main()
{   fin >> n;
    for (i=2;i<=n;++i)
        prim[i] = true;
    for (i=2;i<=n;++i)
        if (prim[i])
        {   ++rasp;
            for (j=i+i;j<= n;j+= i)
                prim[j] = false;
        }
	fout << rasp;
    return 0;
}