# 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]

encoded = txt[0]
for i in range(1, len(txt)):
    val = sum(ascii_codes[:i]) % K
    val += ascii_codes[i]
    if val > 90:
        val -= 26
    encoded += chr(val)

print(encoded)