#include<bits/stdc++.h> using namespace std; int minn=1001,maxn=-1001,g[1010][15],piao[15],last_piaoshu,last_pinpai,n,m; bool st[15],success=true; void pingxuan(){ while(true){ memset(piao,0,sizeof(piao)); for(int i=1;i<=n;i++){ for(int j=1;j<=m;j++){ int k=g[i][j]; if(k==0)break; if(st[k])continue; piao[k]++; break; } } for(int i=1;i<=m;i++){ if(piao[i]<minn&&!st[i])minn=piao[i]; if(piao[i]>maxn&&!st[i])maxn=piao[i]; } if(maxn>minn){ for(int i=1;i<=m;i++)if(piao[i]==minn&&st[i]==false)st[i]=true;//品牌出局(bushi) continue; }else{ int sum=0; for(int i=1;i<=m;i++)if(piao[i]==minn)sum++,last_pinpai=i; if(sum==1)return; else{ last_piaoshu=minn; success=false; return; } } } } int main(){ cin>>m>>n; for(int i=1;i<=n;i++){ string str; cin>>str; for(int j=0;j<str.length();j++){ g[i][j+1]=str[j]-'0'; } } pingxuan(); if(success)cout<<last_pinpai<<endl; else cout<<'-'<<last_piaoshu<<endl; return 0; }