#include <stdlib.h> //for atoi()
#include <stdio.h> //for printf()
#include <unistd.h> //for read()
#include <math.h> //for sqrt()

 int isPrime(int num) {
    if(num <= 1)
        return 0;
    if (num <= 3)
        return 1; 
    int range = sqrt(num);
    if (num % 2 == 0 || num % 3 == 0) 
        return 0; 
    for (int i = 5; i <= range; i += 6) 
        if (num % i == 0 || num % (i + 2) == 0) 
            return 0; 
    return 1;
}

int main(void) {
  char buffer[255] = {0};
  int read_count = read(STDIN_FILENO, buffer, 255);
  int number;
  if (read_count == 0) {
    printf("Input empty. Assume the starting number is 1.\n");
    number = 1;
  }
  else {
    number = atoi(buffer);
    printf("Starting number is %i.\n", number);
  }
  int distance = 0;
  while(1) {
    number++;
    if (isPrime(number)) {
      distance++;
      if (number % 10 == 1) break;
    }
  }
  printf("Next prime ending in 1 is %i\n", number);
  printf("Distance is %i primes\n", distance);
  return 0;
}