"""
[19982: ](https://www.acmicpc.net/problem/19982)
Tier: Bronze 2
Category: 구현
"""
def solution():
n = int(input())
a, b, c = map(int,input().split())
ans = ""
for i in range(a):
ans += chr(65 + i % 26)
for i in range(b):
ans += chr(97 + i % 26)
for i in range(n - (a + b)):
ans += chr(48 + i % 10)
return ans
if __name__ == '__main__':
print(solution())