#include <fstream>
using namespace std;
bool v[2000000000];
long n;
ifstream f("ciur.in");
ofstream o("ciur.out");
void ciur()
{
f>>n;
long c=0;
for (long i=2;i<=n;i++)
    v[i]=false;
for (long i=2;i<=n;i++)
    if (v[i]) {for (long j=i*2;j<=n;j++) v[j]=0;c++;}
o<<c;
}
int main()
{
ciur();
return 0;
}