#include<iostream>
#include<math.h>
using namespace std;
bool IsPrime(int num){
    if (num < 2) return false;
    else if (num == 2) return true;
    else if (num % 2 == 0) return false; 

    double sqrtNum = sqrt(num);
    for (int i = 3; i <= sqrtNum; i += 2)
    {
        if (num % i == 0)
            return false;
    }
    return true;
}
int main() {
  int n;
  int sum[1000000];
  sum[0]=0;
  sum[1]=0;
  sum[2]=1;
  for(int i=3;i<1000000;i++) {
    sum[i]=sum[i-1];
    if(IsPrime(i)) 
      sum[i]++;
 }
  while(cin>>n)
    cout<<sum[n]<<endl;
  return 0;
}

