import std.conv, std.functional, std.range, std.stdio, std.string; import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons; import core.bitop; class EOFException : Throwable { this() { super("EOF"); } } string[] tokens; string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; } int readInt() { return readToken.to!int; } long readLong() { return readToken.to!long; } string COLOR(string s = "") { return "\x1b[" ~ s ~ "m"; } bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } } bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } } int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; } int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); } int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); } enum A = 26; void main() { try { for (; ; ) { const N = readInt; auto S = new string[N]; foreach (i; 0 .. N) { S[i] = readToken; } auto f = new int[][](N, A); foreach (i; 0 .. N) { foreach (s; S[i]) { ++f[i][s - 'a']; } } f.sort; foreach (i; 0 .. N) foreach (b; 0 .. A) { auto gs = f[i].dup; ++gs[b]; const pos = f.lowerBound(gs); if (pos < N && f[pos] == gs) { // bad } else { foreach (a; 0 .. A) foreach (_; 0 .. gs[a]) write(cast(char)('a' + a)); writeln; goto found; } } writeln(-1); found: } } catch (EOFException e) { } }