#include<iostream>
#include<cstdio>
using namespace std;
char c[2000001],nr;
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n,i,j;
    cin>>n;
    for(i=2;i<=n;i++)
        c[i]=1;
    for(i=2;i<=n;i++)
    {
        if(c[i]!=0)
        {
            nr++;
            for(j=i+i;j<=n;j+=i)
            {
                c[j]=0;
            }
        }
    }
    cout<<nr;
    return 0;
}