a=raw_input().split()
c=[]
for b in a:
    c.append(int(b))
i=1
x=0
z=1
schetchik2=1
schetchik=0
shag=1
if len(c)==1:
    print "yes"
else:
    while c[i-1]==c[i] and i<len(c)-1:
        shag+=1
        i+=1
    hi = c[shag]-c[shag-1]
    while x<shag:
        if c[x:len(c):shag]==c[0:len(c):shag]:
            schetchik+=1
        x+=1
    if shag == len(c)-1:
        print "yes"
    else:
        while z< (len(c)/shag):
            if (c[z*shag]-c[(z*shag)-1])**2 == hi*hi:
                schetchik2+=1
            z+=1
        if (schetchik == shag and schetchik2 == len(c)/shag):
            print "yes"
        else:
            print "no"