数列求值4 - Problem - MYOJ

Problem S: 数列求值4

Problem S: 数列求值4

_{[Creator : ]}

Time Limit : 1.000 sec Memory Limit : 256 MiB

Submit ProblemList Solved: 8 Submit Num: 11 Statistics ShowOff!

Description

数列A1,A2,A3,A4,…,A20
已知

A1=0
A2=1
A3=1
A4=A1+2∗A2＋A3
A5=A2+2∗A3+A4
求An

Input

输入一行，包含一个整数n

Output

输出一行，包含一个整数

Constraints

1≤n≤20

Sample 1 Input

Sample 1 Output

Submit