#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
string to_string(pair<A, B> p);
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
string to_string(const string& s) {
  return '"' + s + '"';
}
string to_string(const char* s) {
  return to_string((string) s);
}
string to_string(bool b) {
  return (b ? "true" : "false");
}
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
void debug_out() { cout << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cout << " " << to_string(H);
  debug_out(T...);
}
#ifdef LOCAL
#define dbg(...) cout << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define dbg(...) 42
#endif
const long long mod = 1e9+7; // CHECK
long long power(long long a, long long b, long long m = mod) {
    if(b < 0) {
        return power(power(a, -b), mod-2);
    }
    long long x = 1;
    while(b) {
        if(b & 1) {
            x = 1ll * x * a % m;
        }
        a = 1ll * a * a % m;
        b /= 2;
    }
    return x;
}
#define ll long long
const int INT_INF = 1e9+9;
const ll LL_INF = 2e18;
const int N = 3e5+9; // check N, mod

signed main() {  
    ios_base::sync_with_stdio(false); 
    cin.tie(0); cout.tie(0);
    string s; cin >> s;
    if (s == "zyxwvutsrqponmlkjihgfedcba") {
        cout << "-1\n";
        return 0;
    }
    int n = (int) s.size();
    if (n == 26) {
        int ind = -1;
        for (int i = n-2; i >= 0; i--) {
            if (s[i] < s[i+1]) {
                ind = i;
                break;
            }
        }
        char now;
        for (int i = n-1; i > ind; i--) {
            if (s[i] > s[ind]) {
                now = s[i];
                break;
            }
        }
        cout << s.substr(0, ind) << now << endl;
    } else {
        vector<int> oc(27);
        for (int i = 0; i < n; i++) {
            oc[s[i]-'a']=1;
        }
        int mex = 0;
        while (oc[mex]) mex++;
        cout << s << char('a' + mex) << endl;
    }
    

    return 0;
}


#include <stdio.h>
#include <string>
#include <string.h>
#include <cstring>
#include <algorithm>

using namespace std;
int a;
char test[21];
char temp;

int main()
{
	scanf("%s",test);
	for(a=strlen(test)-1;a>=0;a--)
	{
	printf("%c",test[a]);
	}
	printf("\n");
	return 0; 
}