#include <cstdio>
#include <iostream>
#include <bitset>
#define nmax 2000010
using namespace std;

int n,nr;
bitset<nmax> is;

inline void ciur(int val)
{
    for(int i=val;i<=n;i+=val) is[i]=1;
}

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    cin>>n;
    if(n==1) { cout<<0<<'\n'; return 0;}
    nr=1; ciur(2);
    for(int i=3;i<=n;i+=2)
        if(!is[i])
        {
            nr++;
            ciur(i);
        }
    cout<<nr<<'\n';
    fclose(stdin);
    fclose(stdout);
    return 0;
}