#include<stdio.h>
char v[2000000];
int main() {
  FILE *fin, *fout;
  int n, i, nrprime, j;

  fin = fopen("ciur.in", "r");
  fout = fopen("ciur.out", "w");
  fscanf(fin, "%d", &n);
  nrprime = 0;
  for(i = 0; i <= n; i++) {
    v[i] = 1;
  }
  for(i = 2;i < n; i++) {
    if(v[i] == 1) {
      nrprime++;
      for(j = i * 2; j < n; j = j + i) {
        v[j] = 0;
      }
    }
  }
  fprintf(fout, "%d ", nrprime);

  fclose(fin);
  fclose(fout);

  return 0;
}