#include<iostream>
#include<vector>
using namespace std;
int main(void){
  int n;
while(cin>>n){
  vector<bool> nature(n,true);
  nature[0]=nature[1]=false;
  for(int i=0;i*i<=n;i++){
if(nature[i]){
  for(int j=2;j<=n/i;j++)
  nature[i*j]=false;
}
  }
int count=0;
for(int i=0;i<=n;i++)
if(nature[i])
count++;
cout<<count<<endl;
}
return 0;
}