#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool com[9999999];
int i,n;
int main()
{
    fin>>n;
    for(i=2; i<=n/2; ++i)
    {
        if(com[i] == false)
        {
            int j = i+i;
            while(j<=n)
            {
                com[j]=true;
                j += i;
            }
        }
    }
    int nr=0;
    for(i=n; i--; i>=2)
        if(com[i] == false)
        nr++;
    fout<<nr-2;
}