#include<iostream>
#include<cmath>
#include<string.h>
#include<vector>
#include<algorithm>
#include<cstdio>
#include<queue>
using namespace std;
#define xx return
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define dwn(i,a,b) for(int i=(a);i>=(b);i--)
const int N=1020;

int n;
char s[101][101];
int in[30];
char ans[30];
int h[N],e[N*2],ne[N*2],idx=0;
bool flg=0;

inline void add(int a,int b)
{
	in[b]++;
	e[++idx]=b,ne[idx]=h[a],h[a]=idx;
}

void topsort()
{
	queue<int>q;
	rep(i,1,26)if(!in[i])q.push(i);
	int cnt=0;
	int tot=0;
	while(q.size())
	{
		int u=q.front();q.pop();cnt++;
		ans[++tot]=u+'a'-1;
		for(int i=h[u];i;i=ne[i])
		{
			if(--in[e[i]]==0)q.push(e[i]);
		}
	}
	if(cnt==26)
	{
		cout<<ans+1;
		xx;
	}
	else {
		puts("Impossible");xx;
	}
}

inline void solve()
{
	scanf("%d",&n);
	rep(i,1,n)
	{
		scanf("%s",s[i]);
	}
	rep(i,1,n)
	{
		rep(j,1,i-1)
		{
			if(strlen(s[j])>strlen(s[i]))
			{
				bool f=0;
				rep(k,0,strlen(s[i])-1)
				{
					if(s[i][k]!=s[j][k])
					{
						f=1;break;
					}
				}
				if(!f){
					flg=1;break;
				}
			}
			rep(k,0,min(strlen(s[j]),strlen(s[i]))-1)
			{
				if(s[i][k]!=s[j][k])
				{
					add((s[j][k]-'a'+1),(s[i][k]-'a'+1));
					break;
				}
			}
		}
		if(flg)break;
	}
	if(flg){
		puts("Impossible");xx;
	}
	topsort();
	xx;
}

signed main()
{
	solve();
	xx 0;
}

wa *12,玄关求调