#include <stdio.h>
 
int main() {
 
  int n,i,j;
  int count;
  while(1) {
    scanf("%d",&n);
 
    if(n == 0) break;
    count = 0;
    for(i=n+1;i<=2*n;i++) {
 
      for(j=2;j*j<=i;j++) {
    if(i % j ==0) break;
      }
 
      if(j*j >i) count++;
 
    }
 
    printf("%d\n",count);
 
 
  }
  return 0;
 
}