#include <iostream>
using namespace std;

char primes[200000];
int i, j, n, nr;

int main()
{
    cin>>n;
    for (i=1;2*i+1<=n;i++)
    {
        if ((primes[i/8]&1<<(7-i%8))==0)
        {
            nr++;
            for (j=((2*i+1)*(2*1+1)-1)/2;2*j+1<=n;j+=i*2+1)
            {
                primes[j/8] |= 1<<(7-j%8);
            }
        }
    }
    cout<<nr+1;

return 0;
}