#include <fstream>

int main() {
   int n, s=0;
   std::ifstream("ciur.in") >> n;
   bool * p = new bool[n + 1];
   for(int i = 2; i <= n; i++)
      p[i] = true;
   for(int i=2; i <= n; i++)
      if(p[i])
         for(int j = 2; i * j <= n; j++)
            p[i * j] = false;
   for(int i = 2; i <= n; i++)
      s += p[i];
   std::ofstream("ciur.out") << s;
}