#include <bits/stdc++.h>
using namespace std;
template <class T>
inline bool gmin(T &a, T b) {
  if (a > b) return a = b, true;
  return false;
}
template <class T>
inline bool gmax(T &a, T b) {
  if (a < b) return a = b, true;
  return false;
}
template <class T>
T exgcd(T a, T b, T &first, T &second) {
  if (!b)
    return first = (T)1, second = (T)0, a;
  else {
    T d = exgcd(b, a % b, second, first);
    return second -= a / b * first, d;
  }
}
const int INF = 0x3f3f3f3f;
const long long LINF = 0x3f3f3f3f3f3f3f3fll;
const double DINF = 1e10;
const double EPS = 1e-9;
const double PI = 3.14159265358979323846264338327950288;
inline int dcmp(const double &a) { return a > EPS ? 1 : (a < -EPS ? -1 : 0); }
const int MAXN = 1005;
int n, m;
int cnt[MAXN];
char s[MAXN];
int main() {
  scanf("%s", s);
  scanf("%d", &n);
  int m = strlen(s);
  for (int i = 0; i <= m - 1; i++) cnt[s[i] - 'a']++;
  int tot = 0;
  for (int i = 0; i <= 25; i++)
    if (cnt[i]) tot++;
  if (n < tot)
    printf("-1\n");
  else {
    for (int ans = 1; ans <= m; ans++) {
      int rest = n;
      for (int i = 0; i <= 25; i++)
        if (cnt[i]) {
          rest -= cnt[i] / ans + (cnt[i] % ans != 0);
        }
      if (rest >= 0) {
        printf("%d\n", ans);
        for (int i = 0; i <= 25; i++)
          if (cnt[i]) {
            for (int j = 1; j <= cnt[i] / ans + (cnt[i] % ans != 0); j++)
              printf("%c", i + 'a');
          }
        for (int i = 1; i <= rest; i++) printf("a");
        printf("\n");
        break;
      }
    }
  }
  return 0;
}
