#include<iostream>#include<cstdio>#include<vector>#include<queue>#include<algorithm>#include<cstring>using namespace std;queue<int>q;int n;vector<int>graph[110];string s[110];int mp[30][30];int in[30];void toposort(){    for(int i=0;i<26;i++)         if(!in[i])        {cout<<(char)(i+‘a‘);q.push(i);}//    if(!flag){cout<<"Impossible"<<endl;return;}    while(!q.empty())    {        int u=q.front();q.pop();        for(int i=0;i<graph[u].size();i++)        {            int v=graph[u][i];            in[v]--;            if(in[v]==0){cout<<(char)(v+‘a‘);q.push(v);}        }    }    for(int i=0;i<26;i++) if(in[i]==-1)cout<<(char)(i+‘a‘);    }int main(){    cin>>n;    if(n==1){for(char c=‘a‘;c<=‘z‘;c++) cout<<c;return 0;}     for(int i=1;i<=n;i++)        cin>>s[i];    memset(in,-1,sizeof(in));    for(int i=n;i>=1;i--)for(int j=i-1;j>=1;j--)    {        int l=0;        while(s[i][l]==s[j][l]&&l<=min(s[i].length(),s[j].length())) l++;        if(l==s[i].length())        {            cout<<"Impossible"<<endl;            return 0;        }        if(l==s[j].length())continue;        mp[s[i][l]-‘a‘][s[j][l]-‘a‘]=1;        if(in[s[j][l]-‘a‘]==-1)in[s[j][l]-‘a‘]=0;        in[s[i][l]-‘a‘]+=in[s[i][l]-‘a‘]==-1?2:1;        graph[s[j][l]-‘a‘].push_back(s[i][l]-‘a‘);        }            for(int k=0;k<26;k++)        for(int i=0;i<26;i++)            for(int j=0;j<26;j++)                mp[i][j]+=mp[i][k]*mp[k][j];    for(int i=0;i<26;i++)        if(mp[i][i]){cout<<"Impossible"<<endl;return 0;}    toposort();    return 0;}