#include <bits/stdc++.h>
#define DM 2000001
#define ll long long
using namespace std;
bitset<DM> isp;

int main()
{
    int n,cont=0;
    cin>>n;

    isp[1]=1;
    for(ll i=2;i<=n;++i)
        if(!isp[i])
        {
            cont++;
            for(ll j=i*i;j<=n;j+=i)
                isp[j]=1;
        }

    cout<<cont;
    return 0;
}