1. int read()
    2. {
    3.  int x = 0, f = 1;
    4.  char c = getchar();
    5.  while (c < '0' || c>'9') { 
    6.      if (c == '-') f = -1; 
    7.      c = getchar(); 
    8.  }
    9.  while (c >= '0' && c <= '9')
    10.     x = x * 10 + c - '0';
    11.     c = getchar();
    12.  return x * f;
    13. }