#include <stdio.h>

int main(){

FILE *file1, *file2;
int n, i, j, nr = 1;
char p[2000005];

memset(p, 1, 2000005);

file1 = fopen("ciur.in", "r");
file2 = fopen("ciur.out", "w");

fscanf(file1, "%d", &n);

  for (i = 1; ((i * i) << 1) + (i << 1) <= n; i += 1) {
    if (p[i] == 0) {
      for (j = ((i * i) << 1) + (i << 1); (j << 1) + 1 <= n; j += (i << 1) + 1) {
        p[j] = 1;
      }
    }
  }
  for (i=1; 2 * i + 1 <= n; ++i)
      if (p[i] == 0) nr++;

fprintf(file2, "%d", nr);

return 0;
}