Go: package main

import "fmt"

var H, W int

type point struct {
	x, y int
}

func (p *point) add(q point) {
	p.x += q.x
	p.y += q.y
	if p.x < 0 {
		p.x += H
	}
	if p.y < 0 {
		p.y += W
	}
	p.x %= H
	p.y %= W
}

func isPalindrome(str string) bool {
	for i, j := 0, len(str)-1; i < j; i, j = i+1, j-1 {
		if str[i] != str[j] {
			return false
		}
	}
	return true
}

func magicSpel(arr []string) string {
	var ans string
	m := map[string]int{}
	for i := range arr {
		for j := range arr[i] {
			for _, d := range []point{{-1, -1}, {-1, 0}, {-1, 1}, {0, -1}, {0, 1}, {1, -1}, {1, 0}, {1, 1}} {
				cur := point{x: i, y: j}
				str := string(arr[cur.x][cur.y])
				cur.add(d)
				for i != cur.x || j != cur.y {
					str += string(arr[cur.x][cur.y])
					cur.add(d)
					if isPalindrome(str) {
						m[str] += 2
					} else {
						m[str]++
					}
				}
			}
		}
	}
	for s, v := range m {
		if 1 < v {
			if len(ans) < len(s) {
				ans = s
			} else if len(ans) == len(s) && s < ans {
				ans = s
			}
		}
	}

	if len(ans) == 0 {
		return "0"
	}

	return ans
}

func main() {
	for {
		fmt.Scan(&H, &W)
		if H == 0 && W == 0 {
			break
		}

		var arr []string

		for i := 0; i < H; i++ {
			var s string
			fmt.Scan(&s)
			arr = append(arr, s)
		}

		fmt.Println(magicSpel(arr))
	}
}

// 2 3
// ABC
// DEF

C++: // >>> TEMPLATES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using i32 = int32_t;
using i64 = int64_t;
using u32 = uint32_t;
using u64 = uint64_t;
#define int ll
#define double ld
#define rep(i,n) for (int i = 0; i < (int)(n); i++)
#define rep1(i,n) for (int i = 1; i <= (int)(n); i++)
#define repR(i,n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep1R(i,n) for (int i = (int)(n); i >= 1; i--)
#define loop(i,a,B) for (int i = a; i B; i++)
#define loopR(i,a,B) for (int i = a; i B; i--)
#define all(x) (x).begin(), (x).end()
#define allR(x) (x).rbegin(), (x).rend()
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fst first
#define snd second
template <class Int> auto constexpr inf = numeric_limits<Int>::max()/2-1;
auto constexpr INF32 = inf<int32_t>;
auto constexpr INF64 = inf<int64_t>;
auto constexpr INF   = inf<int>;
#ifdef LOCAL
#include "debug.hpp"
#else
#define dump(...) (void)(0)
#define say(x) (void)(0)
#define debug if (0)
#endif
template <class T> using pque_max = priority_queue<T>;
template <class T> using pque_min = priority_queue<T, vector<T>, greater<T> >;
template <class T, class = typename T::iterator, class = typename enable_if<!is_same<T, string>::value>::type>
ostream& operator<<(ostream& os, T const& v) { bool f = true; for (auto const& x : v) os << (f ? "" : " ") << x, f = false; return os; }
template <class T, class = typename T::iterator, class = typename enable_if<!is_same<T, string>::value>::type>
istream& operator>>(istream& is, T &v) { for (auto& x : v) is >> x; return is; }
template <class T, class S> ostream& operator<<(ostream& os, pair<T,S> const& p) { return os << "(" << p.first << ", " << p.second << ")"; }
template <class T, class S> istream& operator>>(istream& is, pair<T,S>& p) { return is >> p.first >> p.second; }
struct IOSetup { IOSetup() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); } } iosetup;
template <class F> struct FixPoint : private F {
    constexpr FixPoint(F&& f) : F(forward<F>(f)) {}
    template <class... T> constexpr auto operator()(T&&... x) const { return F::operator()(*this, forward<T>(x)...); }
};
struct MakeFixPoint {
    template <class F> constexpr auto operator|(F&& f) const { return FixPoint<F>(forward<F>(f)); }
};
#define MFP MakeFixPoint()|
#define def(name, ...) auto name = MFP [&](auto &&name, __VA_ARGS__)
template <class T, size_t d> struct vec_impl {
    using type = vector<typename vec_impl<T,d-1>::type>;
    template <class... U> static type make_v(size_t n, U&&... x) { return type(n, vec_impl<T,d-1>::make_v(forward<U>(x)...)); }
};
template <class T> struct vec_impl<T,0> { using type = T; static type make_v(T const& x = {}) { return x; } };
template <class T, size_t d = 1> using vec = typename vec_impl<T,d>::type;
template <class T, size_t d = 1, class... Args> auto make_v(Args&&... args) { return vec_impl<T,d>::make_v(forward<Args>(args)...); }
template <class T> void quit(T const& x) { cout << x << endl; exit(0); }
template <class T, class U> constexpr bool chmin(T& x, U const& y) { if (x > y) { x = y; return true; } return false; }
template <class T, class U> constexpr bool chmax(T& x, U const& y) { if (x < y) { x = y; return true; } return false; }
template <class It> constexpr auto sumof(It b, It e) { return accumulate(b,e,typename iterator_traits<It>::value_type{}); }
template <class T> int sz(T const& x) { return x.size(); }
template <class C, class T> int lbd(C const& v, T const& x) {
    return lower_bound(v.begin(), v.end(), x)-v.begin();
}
template <class C, class T> int ubd(C const& v, T const& x) {
    return upper_bound(v.begin(), v.end(), x)-v.begin();
}
constexpr int popcnt(ll x) { return __builtin_popcountll(x); }
template <class Int> struct Random {
    mt19937_64 mt{random_device{}()};
    //mt19937_64 mt{(unsigned)time(0)};
    Int a,b; // [a,b]
    Random(Int a, Int b) : a(a), b(b) {}
    Int operator()() { return uniform_int_distribution<Int>(a,b)(mt); }
};
template <class Int> Int rand(Int a, Int b) { // [a,b]
    static mt19937_64 mt{random_device{}()};
    return uniform_int_distribution<Int>(a,b)(mt);
}
// <<<
const int dx[] = { 1,0,-1,0,1,-1,-1,1 };
const int dy[] = { 0,1,0,-1,1,1,-1,-1 };

string solve(int n, int m) {
    vector<string> s(n); cin >> s;
    map<string,int> cnt;
    string t;
    dump(n,m);
    rep (i,n) rep (j,m) rep (dir,8) {
        int x = i, y = j;
        t.clear();
        while (true) {
            t += s[x][y];
            if (sz(t) > 1) cnt[t]++;
            x += dx[dir] + n, x %= n;
            y += dy[dir] + m, y %= m;
            if (x == i && y == j) break;
        }
    }

    int ma = 0;
    for (auto const& p : cnt) {
        if (p.snd > 1) chmax(ma, sz(p.fst));
    }
    if (ma == 0) return "0";

    string ans(1,'z'+1);
    for (auto const& p : cnt) {
        if (p.snd > 1 && sz(p.fst) == ma) {
            chmin(ans, p.fst);
        }
    }
    return ans;
}

int32_t main() {
    while (true) {
        int h,w; cin >> h >> w;
        if (h == 0 && w == 0) break;
        cout << solve(h,w) << "\n";
    }
}