#include <iostream>
#include <vector>
#include <cstdlib>
#include <fstream>
#include <cmath>
using namespace std;
bool prime[2000000];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
int N,M;
cin>>N;
prime[2]=0;
prime[1]=1;
int l=0;
for(int x=2;x<=N;x++){
if(!prime[x]){
    l++;
for(int j=x;j<=N;j+=x)
    prime[j]=1;
}
}
cout<<l;
return 0;
}