Code

#方法1
# _=input()
# str=input()
# l=[0 for i in range(26)]
# for c in str:
#     if 0<=ord(c)-65<=25:
#         if l[ord(c)-65]==0:
#             l[ord(c)-65]=1
#     elif 0<=ord(c)-97<=25:
#         if l[ord(c)-97]==0:
#             l[ord(c)-97]=1
# flag=True
# for i in range(26):
#     if l[i]==0:
#         print('NO')
#         flag=False
#         break
# if flag==True:
#     print('YES')
#方法2
_=input()
str=input().lower()
S=set()
for c in str:
    S.add(c)
if len(S)<26:
    print('NO')
else:
    print('YES')