//#undef LOCAL
#include <bits/stdc++.h>
using namespace std;
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
template<class T> using V = vector<T>;
template<class T> using VV = V<V<T>>;
constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n-1); }
#define FOR(i, a, b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,N) for(int i=0;i<(int)(N);i++)
#define rep1(i,N) for(int i=1;i<=(int)(N);i++)
#define fs first
#define sc second
#define eb emplace_back
#define pb eb
#define all(x) x.begin(),x.end()
template<class T, class U> void chmin(T& t, const U& u) { if (t > u) t = u; }
template<class T, class U> void chmax(T& t, const U& u) { if (t < u) t = u; }
#ifdef LOCAL
#define show(x) cerr << __LINE__ << " : " << #x << " = " << (x) << endl
#else
#define show(x) true
#endif
template <class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
 return os << "P(" << p.first << ", " << p.second << ")";
}
template <class T> ostream& operator<<(ostream& os, const V<T>& v) {
 os << "[";
 for (auto d : v) os << d << ", ";
 return os << "]";
}
// cin.tie(nullptr);
// ios::sync_with_stdio(false);
// cout << fixed << setprecision(20);


//境界iを中心とする最長回文の長さ/2
template <class S> V<int> manacher(const S& s) {
  int n = int(s.size());
  V<int> r(n);
  if (n == 0) return r;
  r[0] = 1;
  for (int i = 1, j = 0; i < n; i++) {
    int& k = r[i];
    k = (j + r[j] <= i) ? 0 : min(j + r[j] - i, r[2 * j - i]);
    while (0 <= i - k && i + k < n && s[i - k] == s[i + k]) k++;
    if (j + r[j] < i + r[i]) j = i;
  }
  return r;
}

//文字iを中心とする最長回文の長さ
template <class S> V<int> manacher_even(const S& s) {
  int n = int(s.size());
  V<int> r(n + 1);
  for (int i = 1, j = 0; i < n; i++) {
    int& k = r[i];
    k = (j + r[j] <= i) ? 0 : min(j + r[j] - i, r[2 * j - i]);
    while (0 <= i - 1 - k && i + k < n && s[i - 1 - k] == s[i + k]) k++;
    if (j + r[j] < i + r[i]) j = i;
    }
  return r;
}

int main() {
  int N,M;cin>>N>>M;
  string S,T;cin>>S>>T;
  bool bl=M%2==0;
  for(int m=0;m<M;m++){
    if(T[m]!=T[M-1-m]){
      bl=false;
    }
  }
  const int inf=1<<30;
  int ans=inf;
  if(bl){
    vector<int> man=manacher_even(T),pal(M+1);
    for(int m=0;m<M+1;m++){
      pal[m]=m;
    }
    int r=0;
    for(int m=0;m<M+1;m++){
      while(r<=m+man[m]){
        pal[r]=m;
        r+=1;
      }
      if(S==T){
        ans=0;
      }
      else{
        for(int _=0;_<2;_++){
          int le=0;
          for(int i=0;i<min(S.size(),T.size());i++){
            if(S[i]==T[i]){
              le+=1;
            }
            else{
              break;
            }
          }
          int cnt=0,cur=M;
          while(1){
            if(le*2>=cur){
              ans=min(ans,cnt+1);
              break;
            }
            if(cur<=pal[cur/2]*2){
              break;
            }
            cur=pal[cur/2]*2;
            cnt+=1;
          }
          reverse(S.begin(),S.end());
        }
      }
    }
  }
  if(ans==inf){
    ans=-1;
  }
  cout<<ans<<"\n";
}