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