#include <fstream>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
int n, m, i, j, nr;
bool f[2000005];
int main(){
    cin>>n;
    f[0]=1;
    f[1]=1;
    for(i=2;i<=n;i++){
        if(f[i]==0){
            nr++;
            for(j=i+i;j<=n;j+=i){
                f[j]=1;
            }
        }
    }
    cout<<nr<<" ";
}