题解 | 牛牛的替换

n = list(input().split())
a = list(input())
for i in range(int(n[0])):
    if a[i] == n[1]:
        a[i] = n[2]
        if a[i] == n[3]:
            a[i] = n[4]
    if a[i] == n[3]:
        a[i] = n[4]
print("".join(a))