#include <fstream>
#include <bitset>
#define Nmax 2000099
#define Pmax 200000
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
 
int N, P[Pmax];
bitset < Nmax > v;
 
 
void ciur(int N) {
    P[ ++P[0] ] = 2;
    
    for (int i = 4; i <= N; i += 2) v[i] = 1;
    
    for(int i = 3; i <= N; i +=2)
      if(!v[i]){
         P[ ++P[0] ] = i;
          for(int j = 2*i; j <=N ; j +=i)
                   if(!v[j]) v[j] = 1;
      }
}

int main() {
    f >> N;
    ciur(N);
    g << P[0] << '\n';
    f.close();g.close();
    return 0;
}