#include<bits/stdc++.h>

using namespace std;

#define a(x) x<<1

#define b(x) x<<1|1

#define pb push_back

stack<int>a;

string s[];

vector<int>v[];

int id[],siz[],n,m;

int trie[][],cnt,bel[];

int low[],dfn[],is[],T,sum;

inline bool cmp(int a,int b){return siz[a]<siz[b];}

inline void add(int x,int y){v[x].pb(y),v[y^].pb(x^);}

inline void tarjan(int x,int fa){

    dfn[x]=low[x]=++T;

    a.push(x);

    is[x]=;

    for(int i=;i<v[x].size();i++)

      if(v[x][i]!=fa){

          if(!dfn[v[x][i]]){

            tarjan(v[x][i],x);

            low[x]=min(low[x],low[v[x][i]]);

          }else if(is[v[x][i]]){

            low[x]=min(low[x],dfn[v[x][i]]);

          }

      }

    if(low[x]==dfn[x]){

      sum++;

      while(){

          int u=a.top();

          a.pop();

          is[u]=;

          bel[u]=sum;

          if(u==x)break;

      }

    }

    return;

}

inline void ins(int i,int x){

    int p=,wh,la=;

    for(int j=;j<siz[i];j++){

      wh=(s[i][j]-'');

      if(!trie[p][wh])trie[p][wh]=++cnt;

      la=p,p=trie[p][wh],add(x,a(p));

    }

    trie[la][wh]=++cnt;

    add(x,b(cnt)),add(a(cnt),a(p));

    return;

}

int main(){

    int i,j,k,ok;

    scanf("%d",&n);cnt=n;

    for(i=;i<=n;i++){

      cin>>s[i];

      id[i]=i;

      siz[i]=s[i].length();

    }

    sort(id+,id+n+,cmp);

    for(int _=;_<=n;_++){

      i=id[_],ok=;

      for(j=;j<siz[i];j++)

        if(s[i][j]=='?'){

          s[i][j]='',ins(i,a(i));

          s[i][j]='',ins(i,b(i));

          ok=;

          break;

        }

      if(!ok){

          ins(i,a(i));

          add(b(i),a(i));

      }

    }

    for(i=;i<=(cnt<<|);i++)if(!dfn[i])tarjan(i,);

    for(i=;i<=cnt;i++)

      if(bel[a(i)]==bel[b(i)]){

          puts("NO");

          return ;

      }

    puts("YES");

    return ;

}