//#include <iostream>
#include <fstream>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
int sieve[2000005];
int main()
{
    int cnt=1,n,i,j;
    cin>>n;
    sieve[0]=1;
    sieve[1]=1;
    for(i=4;i<=n;i+=2)
        sieve[i]=1;
    for(i=3;i<=n;i+=2)
    {
        if(sieve[i]==0)
        {
            cnt++;
            for(j=i*i;j<=n;j+=i)
            {
                sieve[j]=1;
            }
        }
    }
    cout<<cnt;
    return 0;
}