#include <fstream>
using namespace std;const int N=2000001;bool c[N];int main(){ifstream fin("ciur.in");ofstream fout("ciur.out");int n;fin>>n;c[0]=c[1]=true;for(int i=2;i*i<=n;i++){if(!c[i]){for(int j=i*i;j<=n;j+=i){c[j]=true;}}}int cnt=0;for(int i=2;i<=n;i++){if(!c[i]) cnt++;}fout<<cnt;fin.close();fout.close();return 0;}