#include <fstream>
#define nmax 2000001
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
int n,ans;
bool ciur[nmax];
int main()
{
    cin>>n;
    for(int i=2;i<=n;i++)
        if(!ciur[i]){
            ans++;
            for(int j=1ll*i*i;j<=n;j+=i)
                ciur[j]=1;
        }
    cout<<ans;
    return 0;
}