#include <bits/stdc++.h>
///O(n log(log n))
using namespace std;
bitset<2000005>a;

int n;

int Ciur(int n)
{
    int i, j;
    a[1] = 1;
    for(i = 4; i <= n; i += 2)
        a[i] = 1;
    for(i = 3; i * i <= n; i += 2)
     if(a[i] == 0)
      for(j = i * i; j <= n; j = j + i * 2)
            a[j] = 1;
    int cnt = 0;
    for(i = 2; i <= n; i++)
        if(a[i] == 0)
            cnt++;
    return cnt;
}

int main()
{
    ifstream f("ciur.in");
    f >> n;
    f.close();
    ofstream g("ciur.out");
    g << Ciur(n) << "\n";
    g.close();
    return 0;
}