# I. 695.
# Rajtik Sándor Barnabás 10. o.
# Budapest, Budapesti Fazekas M. Gyak. Ált. Isk. és Gimn.

K = int(input())
txt = input()

ascii_codes = [ord(char) for char in txt]
orig_codes = []

orig_codes.append(ascii_codes[0])
decoded = txt[0]

for i in range(1, len(txt)):
    val = ascii_codes[i] - sum(orig_codes[:i])%K
    if val < 65:
        val += 26
    orig_codes.append(val)
    decoded += chr(val)

print(decoded)