#include <bits/stdc++.h>
int a[1000001];
int Func(int n) {
  if (n == 0)
    return 0;
  else
    return a[n] + Func(n - 1);
}
int main() {
  a[0] = 0;
  a[1] = 0;
  a[2] = 1;
  for (int i = 3; i <= 1000000; i++) {
    if (i % 2 == 0)
      a[i] = 0;
    else {
      int h = 1;
      for (int j = 3; j * j <= i && h == 1; j += 2) {
        if (i % j == 0) h = 0;
      }
      a[i] = h;
    }
  }
  int n;
  while (~scanf("%d", &n)) {
    printf("%d\n", Func(n));
  }
}
