#include<fstream>
//#include<iostream>
using namespace std;
int N,k;
char a[2000001];
int main()
{
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");
    cin>>N;
    for(int i=2;i<=N;++i)
    {
        if(a[i]==0)
        {
            for(int j=i*i;(j<=N)&&(j>=0);j=j+i)
                a[j]=1;
            ++k;
        }
    }
    cout<<k;
    return 0;
}