x, y = map(int, input().split())

password = []
a = []
for i in range(x):
    s = input()
    for j in s:
        a.append(j)
    password.append(a)
    a = []

l = int(input())

b = [password[0][0]]

i, j = 0, 0

while i + 1 != x and j != y:
    if i + 1 < x and j + 1 < y:
        if x - i - 1 + y - j - 1 == l:
            if password[i + 1][j] > password[i][j + 1]:
                b.append(password[i + 1][j])
                i += 1
            else:
                b.append(password[i][j+1])
                j += 1
        else:
            if password[i + 1][j] < password[i][j + 1]:
                b.append(password[i + 1][j])
                i += 1
            else:
                b.append(password[i][j+1])
                j += 1
    else:
        if i + 1 >= x:
            if j + 1 < y:
                b.append(password[i][j + 1])
                j += 1
        else:
            b.append(password[i + 1][j])
            i += 1

print(b)