题解 | #杨辉三角的变形#

n=int(input())

if n<3:
    print(-1)
elif n%2!=0:
    print(2)
elif n%2==0 and n%4!=0:
    print(4)
elif n%2==0 and n%4==0:
    print(3)
    

是根据strawberryz老师的解析打出来的