#include <iostream>
#include <fstream>

using namespace std;

int n, s;
char a[2000001];

int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    fin>>n;
    for (int i=2;i<=n;i++)
        a[i]=1;
    for (int i=2;i<=n;i++)
        if (a[i])
        {
            s++;
            for (int j=i+i;j<=n;j+=i)
                a[j]=0;
        }
    fout<<s;
    return 0;
}