#include<fstream>
using namespace std;ifstream fin("ciur.in");ofstream fout("ciur.out");int n,i,j,nr;char p[2000011];int main(){fin>>n;for(i=2; i<=n; i++)if(!p[i]){nr++;for(j=i+i; j<=n; j+=i) p[j]=1;}fout<<nr<<'\n';}