#include<fstream>
#include<iostream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,i,j,sol;
char f[2000001];
 
int main()
{
    fin>>n;
    sol=n-1;
    for(i=2;i*i<=n;i++)
        if(f[i]==0)
            for(j=i+i;j<=n;j=j+i)
            {
                if(f[j]==0)
                {
                    sol--;
                }
                f[j]=1;
            }
    fout<<sol;
    fin.close();
    fout.close();
    return 0;
}