#include <fstream>
#define maxim 2000000
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool c[maxim];
int n,a;
int main ()
{
    fin>>n;
    for(int i=2;i*i<maxim&&i<=n;++i){
        if(c[i]==0){
            ++a;
            for(int j=i*i;j<=n;j+=i)
                c[j]=1;
        }
    }
    fout<<a;
    return 0;
}