package main

import (
	"strconv"
	"strings"
	"fmt"
)

func main() {
	var N int
	fmt.Scanf("%d", &N)
	var S = make([]string, N)
	for i := 0; i < N; i++ {
		fmt.Scanf("%s", &S[i])
		S[i]+="{"
	}

	ans := ""
	for {
		minIndex := 0
		current := ""

		for i := 0; i < N; i++ {
			if len(S[i]) == 0 {
				continue
			}
			if current == "" || current > S[i] {
				current = S[i]
				minIndex = i
			}
		}
		if len(S[minIndex]) == 0 {
			break
		}
		if S[minIndex][0] != '{' {
			ans+=string(S[minIndex][0])

		}
		S[minIndex] = S[minIndex][1:]
	}
	fmt.Println(ans)

}



func mapToString(arr []int) []string {
	ret := make([]string, len(arr))
	for i := 0; i < len(arr); i++ {
		ret[i] = strconv.Itoa(arr[i])
	}
	return ret
}

func PrintI(args ...int) {
	fmt.Println(strings.Join(mapToString(args), " "))
}