/*
#include <kyopro/master>
namespace self{entry
void main(){
  LL(H,W);
  RDVL(str,H,s);
  
  grid g(H,W);
  
  str ans{};
  vec<pair<ll,ll>>cand;
  cand.eb(0,0);
  ans+=s[0][0];
  fo(k,H+W-2){
    char min_char='|';
    fe(cand,i,j){
      if(i+1<H)amin(min_char,s[i+1][j]);
      if(j+1<W)amin(min_char,s[i][j+1]);
    }
    
    vec<pair<ll,ll>>nx_cand;
    fe(cand,i,j){
      if(i+1<H)if(s[i+1][j]==min_char){
        if(nx_cand.size()){ // 重複回避
          auto[ni,nj]=nx_cand.back();
          if(ni!=i+1||nj!=j)nx_cand.eb(i+1,j);
        }else{
          nx_cand.eb(i+1,j);
        }
      }
      if(j+1<W)if(s[i][j+1]==min_char){
        nx_cand.eb(i,j+1);
      }
    }
    ans+=min_char;
    swap(cand,nx_cand);
  }
  
  pp(ans);
}}*/

#include<bits/stdc++.h>
#if __has_include(<atcoder/all>)
#endif
using namespace std;
#define eb emplace_back
#define RD(T,...) T __VA_ARGS__;lin(__VA_ARGS__)
#define LL(...) RD(ll,__VA_ARGS__)
#define RDVL(T,n,...) vec<T>__VA_ARGS__;fe(refs(__VA_ARGS__),e)e.get().resizes(n);lin(__VA_ARGS__)
#define fo(i,...) for(auto[i,i##stop,i##step]=for_range<ll>(0,__VA_ARGS__);i<i##stop;i+=i##step)
#define fe(a,e,...) for(auto&&__VA_OPT__([)e __VA_OPT__(,__VA_ARGS__]):a)
#define defpp template<ostream&o=cout>void pp(const auto&...a){[[maybe_unused]]const char*c="";((o<<c<<a,c=" "),...);o<<'\n';}void epp(const auto&...a){pp<cerr>(a...);}
#define entry defpp void main();void main2();}int main(){self::io();self::main();}namespace self{
namespace self{
void io(){cin.tie(nullptr)->sync_with_stdio(0);cout<<fixed<<setprecision(15);}
using ll=long long;
constexpr auto refs(auto&...a){return array{ref(a)...};}
template<class T>constexpr auto for_range(T s,T b){T a=0;if(s)swap(a,b);return array{a-s,b,1-s*2};}
void lin(auto&...a){(cin>>...>>a);}
bool amin(auto&a,const auto&b){return b<a?a=b,1:0;}
template<class A,class B=A>struct pair{
  A a;B b;
  pair()=default;
  pair(A a,B b):a(a),b(b){}
  auto operator<=>(const pair&)const=default;
};
template<class...A>using pack_back_t=tuple_element_t<sizeof...(A)-1,tuple<A...>>;
}
namespace self {
template<class V>istream&operator>>(istream&i,vector<V>&v){fe(v,e)i>>e;return i;}
template<class V>constexpr int depth=0;
template<class T>struct core_t_helper{using type=T;};
template<class T>using core_t=core_t_helper<T>::type;
template<class V>struct vec;
template<int D,class T>struct hvec_helper{using type=vec<typename hvec_helper<D-1,T>::type>;};
template<class T>struct hvec_helper<0,T>{using type=T;};
template<int D,class T>using hvec=hvec_helper<D,T>::type;
template<class V>struct vec:vector<V>{
  static constexpr int D=depth<V>+1;
  using C=core_t<V>;
  using vector<V>::vector;
  void resizes(const auto&...a){if constexpr(sizeof...(a)==D)*this=make(a...,C{});else{ }}
  static auto make(ll n,const auto&...a){
    if constexpr(sizeof...(a)==1)return vec<C>(n,array{a...}[0]);
    else { }
  }
  ll size()const{return vector<V>::size();}
  auto&emplace_back(auto&&...a){vector<V>::emplace_back(std::forward<decltype(a)>(a)...);return*this;}
};
template<class...A>requires(sizeof...(A)>=2)vec(const A&...a)->vec<hvec<sizeof...(A)-2,pack_back_t<A...>>>;
}
namespace self{
struct str:string{
  str()=default;
};
}
namespace self{
struct grid{
  ll H,W;
  grid(ll H,ll W):H(H),W(W){}
};
}
#if __has_include(<atcoder/all>)
#endif
using namespace std;
namespace self{entry
void main(){
  LL(H,W);
  RDVL(str,H,s);

  grid g(H,W);

  str ans{};
  vec<pair<ll,ll>>cand;
  cand.eb(0,0);
  ans+=s[0][0];
  fo(k,H+W-2){
    char min_char='|';
    fe(cand,i,j){
      if(i+1<H)amin(min_char,s[i+1][j]);
      if(j+1<W)amin(min_char,s[i][j+1]);
    }

    vec<pair<ll,ll>>nx_cand;
    fe(cand,i,j){
      if(i+1<H)if(s[i+1][j]==min_char){
        if(nx_cand.size()){ // 重複回避
          auto[ni,nj]=nx_cand.back();
          if(ni!=i+1||nj!=j)nx_cand.eb(i+1,j);
        }else{
          nx_cand.eb(i+1,j);
        }
      }
      if(j+1<W)if(s[i][j+1]==min_char){
        nx_cand.eb(i,j+1);
      }
    }
    ans+=min_char;
    swap(cand,nx_cand);
  }

  pp(ans);
}}