#include <bits/stdc++.h>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
const int lim=2e6+5;
bool ok[lim];
int n,ans;
int main()
{
    in>>n;
    for(int i=2;i<=n;++i)
    if(!ok[i])
    {
        ++ans;
        for(int j=2*i;j<=n;j+=i)
            ok[j]=1;
    }
    out<<ans<<'\n';
    return 0;
}