a,b,c,d = map(int, input().split())
if (abs(a - b)==1):
    x =1
else:
    x = 0
if (abs(a - c)==1):
    x +=1
else:
    x += 0
if (abs(a - d)==1):
    x +=1
else:
    x += 0
if (abs(b - c)==1):
    x +=1
else:
    x += 0
if (abs(b - d)==1):
    x +=1
else:
    x += 0
if (abs(c - d)==1):
    x +=1
else:
    x += 0
if (x == 4):
    print ("Yes")
else:
    print ("No")