#include <bits/stdc++.h>
using namespace std;
char s[1003];
char res[1003];
int n;
int coun[33];
int coun3[33];
int main() {
  scanf("%s", s);
  scanf("%d", &n);
  int i, j;
  for (i = 0; s[i]; i++) coun[s[i] - 'a']++;
  int coun2 = 0;
  for (i = 0; i < 30; i++)
    if (coun[i] > 0) coun2++;
  if (coun2 > n) {
    printf("-1\n");
    return 0;
  }
  int l, r, re;
  l = 0;
  r = 1003;
  int sum = 0;
  while (r - l > 1) {
    sum = 0;
    re = ((l + r) >> 1);
    for (j = 0; j < 30; j++) {
      sum += coun[j] / re;
      if (coun[j] % re != 0) sum++;
    }
    if (sum > n)
      l = re;
    else
      r = re;
  }
  for (j = 0; j < 30; j++) {
    coun3[j] = coun[j] / r;
    if (coun[j] % r != 0) coun3[j]++;
  }
  i = 0;
  for (j = 0; j < 30; j++) {
    while (coun3[j] > 0) {
      res[i++] = j + 'a';
      coun3[j]--;
    }
  }
  printf("%d\n", r);
  while (i < n) res[i++] = 'a';
  printf("%s\n", res);
}
