#include <bits/stdc++.h>

using namespace std;

const int N=2000000+5;

int n;
bool p[N];

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    cin>>n;
    for(int i=2;i<=n;i++)
    {
        p[i]=1;
    }
    for(int i=4;i<=n;i+=2)
    {
        p[i]=0;
    }
    for(int i=3;i*i<=n;i+=2)
    {
        if(p[i])
        {
            for(int j=i*i;j<=n;j+=2*i)
            {
                p[j]=0;
            }
        }
    }
    int ans=0;
    for(int i=1;i<=n;i++)
    {
        if(p[i])
        {
            ans++;
        }
    }
    cout<<ans<<"\n";
    return 0;
}