母牛生小牛问题

设有一头小母牛，从出生第四年起每年生一头小母牛，按此规律，第N年时有几头母牛？

输入：

本题有多组数据。每组数据只有一个整数N，独占一行。(1≤N≤50)

输出：

对每组数据，输出一个整数（独占一行）表示第N年时母牛的数量

-Cow health problems with a calf heifers, from birth each year, starting the fourth year students a small cow, here the law of the N cows a few years? Input: The questions have multiple sets of data. Each set of data is only an integer N, an exclusive line. (1 ≤ N ≤ 50) Output: for each set of data, output an integer (exclusive line) that the N cows when the number of years