#include <fstream>
using namespace std;

int n,h=1;
bool a[2000002];
int main()
{
int i, j;

ifstream fin("ciur.in");
fin>>n;
fin.close();
for(i = 3; i* i <= n; i++)
if (a[i] == 0) // i este prim
for (j = i * i; j <= n; j = j + 2*i)
a[j] = 1;
for (i = 3; i <= n; i += 2)
if (a[i] == 0) h++;

ofstream fout("ciur.out");
fout<<h<<"\n";
fout.close();
return 0;
}