#include <iostream>
#include <vector>

auto *in = fopen("ciur.in", "r"), *out = fopen("ciur.out", "w") ;

int main() {
  int n ;
  fscanf(in, "%d", &n) ;
  std::vector<bool> prim(n + 1, 0) ;
  prim[1] = 1 ;
  int ans(0) ;
  for (int i = 2 ; i <= n ; ++ i) {
    if (!prim[i]) {
      ans ++ ;
      for (long long j = 1ll * i * i ; j <= n ; j += i) {
        prim[j] = 1 ;
      }
    }
  }
  fprintf(out, "%d", ans) ;
}