#include <bits/stdc++.h>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

#define cin fin
#define cout fout

bitset <2000005> prim;
long long n, k;


int main()
{
    cin >> n;
    for(long long i=2; i<=n; i++)
    {
        if(prim[i] == 0)
        {
           k++;
           for(long long j= i + i; j <=n; j = j + i)
           {
               prim[j] = 1;
           }
        }
    }

    cout << k;
}