#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
const int dx[] = { 1,0 };
const int dy[] = { 0,1 };
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int h, w; cin >> h >> w;
	vector<string>s(h);
	rep(i, h)cin >> s[i];
	string ans;
	vector<pair<char, P>>v;
	v.push_back({ s[0][0],{0,0} });
	rep(i, h + w - 1) {
		ans += v[0].first;
		vector<pair<char, P>>tmp;
		rep(j, v.size()) {
			rep(k, 2) {
				int nx = dx[k] + v[j].second.first;
				int ny = dy[k] + v[j].second.second;
				if (nx >= h)continue;
				if (ny >= w)continue;
				tmp.push_back({ s[nx][ny] ,{nx,ny} });
			}
		}
		sort(all(tmp));
		tmp.erase(unique(all(tmp)), tmp.end());
		v.clear();
		rep(j, tmp.size()) {
			if (tmp[0].first == tmp[j].first)v.push_back(tmp[j]);
		}
	}
	cout << ans << endl;
	return 0;
}