import core.bitop;
import std.algorithm;
import std.ascii;
import std.bigint;
import std.conv;
import std.functional;
import std.math;
import std.numeric;
import std.range;
import std.stdio;
import std.string;
import std.random;
import std.typecons;
import std.container;

ulong MOD = 1_000_000_007;
ulong INF = 1_000_000_000_000;
alias sread = () => readln.chomp();
alias t = Tuple!(string, "name", long, "y");

void main()
{
    auto s = sread();
    auto alphabet = new long[]('z' - 'a' + 1);
    foreach(e; s)
    {
        alphabet[e - 'a']++;
    }
    if(alphabet.sum() < alphabet.length)
    {
        auto c = alphabet.firstNotZero();
        s ~= ('a' + c).to!(char);
        s.writeln();
    }
    else
    {
        long j = s.length - 1;
        while(s[j - 1] > s[j])
        {
            j--;
            if (j < 1)
            {
                writeln(-1);
                return;
            }
        }
        auto tmp = s[j .. $];
        sort(cast(ubyte[]) tmp);
        s = s[0 .. j - 1] ~ tmp[0];
        s.writeln();
    }
}

auto firstNotZero(long[] ary)
{
    long c = -1;
    foreach(i, e; ary)
    {
        if(e == 0)
        {
            c = i;
            break;
        }
    }
    return c;
}

T lread(T = long)()
{
    return readln.chomp.to!T();
}

T[] aryread(T = long)()
{
    return readln.split.to!(T[])();
}

void scan(TList...)(ref TList Args)
{
    auto line = readln.split();
    foreach (i, T; TList)
    {
        T val = line[i].to!(T);
        Args[i] = val;
    }
}
