#!/usr/bin/env python3

r, c = map(int, input().split())
grid = [list(input().rstrip('\n')) for _ in range(r)]

result = []
for i in range(c):
  for j in range(r):
    ch = grid[j][i]
    if 'A' <= ch <= 'Z':
      result.append(ch)
      break
print(''.join(result))