n=int(input())
list=[]
for i in range(n):
    list.append(str(input()))
    i=i+1
    
for i in range(n-1):
    if list[i]==list[i+1]:
        m=list[i+1]
        l=list[i+2]
        list[i+1]=l
        list[i+2]=m
        
    i=i+1
m=0
for i in range(n-1):
    if list[i]==list[i+1]:
        m=m+1
        
    i=i+1

if m>0:
    print("NO")
else:
    print("YES")