n = int(input())

a = []

for i in range(n):

a.append(list(input()))

for i in range(1,n-1):

for j in range(1,n-1):
    if a[i][j] > a[i+1][j] and a[i][j] > a[i-1][j] and a[i][j] > a[i][j+1] and a[i][j] > a[i][j+1]:
        a[i][j]="X"

for i in range(n):

print("".join(str(x) for x in a[i]))

Can you tell me what the error is?