Consider the following recursive implementation used to find the length of a string:#includeint recursive_get_len(char *s, int len){      if(s[len] == 0)        return 0;      return ________;}int main(){      char *s = "abcdef";      int len = recursive_get_len(s,0);      printf("%d",len);      return 0;}Which of the following lines should be inserted to complete the above code?