n=int(input())
l=[int(x) for x in input().split()]
nl=list(set(l))
c="YES"
if len(nl)==len(l):
    nl.sort()
    a=(nl[-1]-nl[0])/(n-1)

    for i in range(n-1):
        if nl[i+1]-nl[i]!=a:
            c="NO"
            break
else:
    c="NO"
print(c)