#!/bin/python3

import math
import os
import random
import re
import sys
import string
from collections import defaultdict

class Decoder:
    _symbols = string.punctuation

    def __init__(self, trigram_list):
        self.final_string = ""
        self.base_string = ""
        self.trigram_list = trigram_list
        self.first_alphanumeric_pos = -1
        self.last_alphanumeric_pos = -1
        self.run_decoder()

    def run_decoder(self):
        self.construct_base_string()
        self.construct_final_string()

    def is_symbol(self, element):
        return element in self._symbols

    def update_first_alphanumeric_pos(self, position):
        self.first_alphanumeric_pos = position
        return True

    def update_last_alphanumeric_pos(self, position):
        self.last_alphanumeric_pos = position
        return True

    def remove_symbols(self):
        string_range = self.base_string[self.first_alphanumeric_pos: self.last_alphanumeric_pos]
        string_range_sanitized = re.sub(f"[{self._symbols}]", " ", string_range).replace("  ", " ")
        return string_range_sanitized

    def construct_final_string(self):
        for position, element in enumerate(self.base_string):
            self.first_alphanumeric_pos == -1 and not self.is_symbol(element) and self.update_first_alphanumeric_pos(
                position)
            element != " " and not self.is_symbol(element) and self.update_last_alphanumeric_pos(position + 1)

        first_string_part = self.base_string[:self.first_alphanumeric_pos]
        second_string_part = self.remove_symbols()
        final_string_part = self.base_string[self.last_alphanumeric_pos:]

        self.final_string = first_string_part + second_string_part + final_string_part

        return self.final_string

    def construct_base_string(self):
        trigrams_ = enumerate(self.trigram_list)
        trigrams_ = {
            pos: dict(enumerate(trigram))
            for pos, trigram in trigrams_
        }
        join_by_index = defaultdict(list)
        for symbols in trigrams_.values():
            for pos, symbol in symbols.items():
                join_by_index[pos] += symbol

        values = []
        for v in join_by_index.values():
            values += v

        self.base_string = "".join(values)


first_multiple_input = input().rstrip().split()

n = int(first_multiple_input[0])

m = int(first_multiple_input[1])

matrix = []

for _ in range(n):
    matrix_item = input()
    matrix.append(matrix_item)
    
    
decorder = Decoder(matrix)
print(decorder.final_string)