#include <iostream>
#include <fstream>
using namespace std;ifstream fin ("ciur.in");ofstream fout("ciur.out");const int N=2000000;bool ciur[N+1];int cnt=0;int implciur(int n){int j,d;for(d=2;d*d<=n;d++){if(ciur[d]==0){for(j=d*d;j<=n;j+=d){if(ciur[j]!=1)cnt--;ciur[j]=1;}}}cnt--;return cnt;}int main(){int n;fin>>n;cnt=n;fout<<implciur(n);return 0;}