#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <iostream>
#include <sstream>
#include <vector>
#include <string>
#include <math.h>
#include <queue>
#include <list>
#include <algorithm>
#include <map>
#include <set>
#include <stack>
#include <ctime>
using namespace std;

#define ALL(c) (c).begin(),(c).end()
#define IN(x,c) (find(c.begin(),c.end(),x) != (c).end())
#define REP(i,n) for (int i=0;i<(int)(n);i++)
#define FOR(i,a,b) for (int i=(a);i<=(b);i++)
#define INIT(a,v) memset(a,v,sizeof(a))
#define SORT_UNIQUE(c) (sort(c.begin(),c.end()), c.resize(distance(c.begin(),unique(c.begin(),c.end()))))
template<class A, class B> A cvt(B x) { stringstream ss; ss<<x; A y; ss>>y; return y; }

typedef pair<int,int> PII;
typedef long long int64;

int n;
string s[300];
vector<int> nc[300];
int deg[300];

int main() {
	cin >> n;
	REP (i,n) cin >> s[i];
	int ok=1;
	REP (i,n) {
		REP (j,i) {
			int k=0;
			while (k<s[i].size() && k<s[j].size() && s[i][k]==s[j][k]) k++;
			if (k<s[i].size() && k<s[j].size()) {
				int ci=s[i][k], cj=s[j][k];
				nc[cj].push_back(ci);
				deg[ci]++;
			} else {
				if (s[j].size()>s[i].size()) ok=0;
			}
		}
	}
	queue<int> q;
	FOR (c,'a','z') {
		if (deg[c]==0) q.push(c);
	}
	string r="";
	while (!q.empty()) {
		char c=q.front(); q.pop();
		r+=c;
		for (int d : nc[c]) {
			deg[d]--;
			if (deg[d]==0) q.push(d);
		}
	}
	if (r.size()!=26) ok=0;
	if (!ok) cout << "Impossible" << endl;
	else cout << r << endl;
	return 0;
}