#include <bits/stdc++.h>
using namespace std;
char s[20005];
struct SuffixArray {
  int wa[20005], wb[20005], cnt[20005], wv[20005];
  int rk[20005], height[20005];
  int sa[20005];
  bool cmp(int r[], int a, int b, int l) {
    return r[a] == r[b] && r[a + l] == r[b + l];
  }
  void calcSA(char r[], int n, int m) {
    int i, j, p, *x = wa, *y = wb;
    for (i = 0; i < m; ++i) cnt[i] = 0;
    for (i = 0; i < n; ++i) cnt[x[i] = r[i]]++;
    for (i = 1; i < m; ++i) cnt[i] += cnt[i - 1];
    for (i = n - 1; i >= 0; --i) sa[--cnt[x[i]]] = i;
    for (j = 1, p = 1; p < n; j *= 2, m = p) {
      for (p = 0, i = n - j; i < n; ++i) y[p++] = i;
      for (i = 0; i < n; ++i)
        if (sa[i] >= j) y[p++] = sa[i] - j;
      for (i = 0; i < n; ++i) wv[i] = x[y[i]];
      for (i = 0; i < m; ++i) cnt[i] = 0;
      for (i = 0; i < n; ++i) cnt[wv[i]]++;
      for (i = 1; i < m; ++i) cnt[i] += cnt[i - 1];
      for (i = n - 1; i >= 0; --i) sa[--cnt[wv[i]]] = y[i];
      for (swap(x, y), p = 1, x[sa[0]] = 0, i = 1; i < n; ++i)
        x[sa[i]] = cmp(y, sa[i - 1], sa[i], j) ? p - 1 : p++;
    }
  }
  void calcHeight(char r[], int n) {
    int i, j, k = 0;
    for (i = 0; i <= n; ++i) rk[sa[i]] = i;
    for (i = 0; i < n; height[rk[i++]] = k)
      for (k ? k-- : 0, j = sa[rk[i] - 1]; r[i + k] == r[j + k]; k++)
        ;
  }
  bool solve(int k, int n, int div) {
    int ca = 0, cb = 0;
    for (int i = 1; i <= n; i++) {
      if (height[i] < k) {
        if (ca == 1 && cb == 1) return true;
        ca = 0;
        cb = 0;
        if (sa[i] < div)
          ca++;
        else if (sa[i] > div)
          cb++;
        continue;
      }
      if (sa[i] < div)
        ca++;
      else if (sa[i] > div)
        cb++;
    }
    return ca == 1 && cb == 1;
  }
} suf;
char a[20005], b[20005];
int main() {
  scanf("%s %s", a, b);
  int n = strlen(a), m = strlen(b);
  strcpy(s, a);
  s[n] = '#';
  strcpy(s + n + 1, b);
  int tot = n + m + 1;
  suf.calcSA(s, tot + 1, 128);
  suf.calcHeight(s, tot);
  int ret = -1;
  for (int i = 1; i <= n; i++) {
    if (suf.solve(i, tot, n)) {
      ret = i;
      break;
    }
  }
  printf("%d\n", ret);
  return 0;
}
