#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math")
#include <bits/stdc++.h>
using namespace std;
template<class t> inline t read(t &x){
	char c=getchar();bool f=0;x=0;
	while(!isdigit(c)) f|=c=='-',c=getchar();
	while(isdigit(c)) x=(x<<1)+(x<<3)+(c^48),c=getchar();
	if(f) x=-x;return x;
}
template<class t,class ...A> inline void read(t &x,A &...a){
	read(x);read(a...);
}
template<class t> inline void write(t x){
	if(x<0) putchar('-'),write(-x);
	else{if(x>9) write(x/10);putchar('0'+x%10);}
}

const int N=1e5+5;
int n,m,tp[N],a[N],b[N];
long long ans;

void GG(){
	write(-1);
	exit(0);
}

signed main(){
	read(n,m);
	for(int i=1;i<=n;i++) read(tp[i]),a[i]=tp[i]-tp[i-1]-1;a[n+1]=m-tp[n];
	for(int i=1;i<=n;i++) read(tp[i]),b[i]=tp[i]-tp[i-1]-1;b[n+1]=m-tp[n];n++;
	for(int i=1,j=1;i<=n;i++) if(b[i]){
		while(!a[j]) j++;
		int cur=0,l=j;
		while(j<=n&&cur<b[i]) cur+=a[j++];
		if(cur>b[i]) GG();
		ans+=max(i-l,0)+max(j-1-i,0);
	}
	write(ans);
}
#include <bits/stdc++.h>

using namespace std;


using int64 = long long;
const int mod = 998244353;

const int64 infll = (1LL << 62) - 1;
const int inf = (1 << 30) - 1;

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} iosetup;


template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << p.first << " " << p.second;
  return os;
}

template<typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
  for (int i = 0; i < (int) v.size(); i++) {
    os << v[i] << (i + 1 != v.size() ? " " : "");
  }
  return os;
}

template<typename T>
istream &operator>>(istream &is, vector<T> &v) {
  for (T &in : v) is >> in;
  return is;
}

template<typename T1, typename T2>
inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }

template<typename T1, typename T2>
inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

template<typename T = int64>
vector<T> make_v(size_t a) {
  return vector<T>(a);
}

template<typename T, typename... Ts>
auto make_v(size_t a, Ts... ts) {
  return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

template<typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill_v(T &t, const V &v) {
  t = v;
}

template<typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill_v(T &t, const V &v) {
  for (auto &e : t) fill_v(e, v);
}

template<typename F>
struct FixPoint : F {
  FixPoint(F &&f) : F(forward<F>(f)) {}

  template<typename... Args>
  decltype(auto) operator()(Args &&... args) const {
    return F::operator()(*this, forward<Args>(args)...);
  }
};

template<typename F>
inline decltype(auto) MFP(F &&f) {
  return FixPoint<F>{forward<F>(f)};
}


int main() {
  int N, L;
  cin >> N >> L;
  vector< int > A(N + 2), B(N + 2);
  for(int i = 1; i <= N; i++) cin >> A[i];
  for(int i = 1; i <= N; i++) cin >> B[i];
  A[N + 1] = L + 1;
  B[N + 1] = L + 1;
  for(int i = 0; i < N + 2; i++) A[i] -= i;
  for(int i = 0; i < N + 2; i++) B[i] -= i;

  map< int, int > ls, rs;
  for(int i = 0, j; i < N + 2; i = j) {
    for(j = i; j < N + 2 and A[i] == A[j]; j++) ;
    ls[A[i]] = i;
    rs[A[i]] = j;
  }
  int64 ret = 0;
  for(int i = 0, j; i < N + 2; i = j) {
    for(j = i; j < N + 2 and B[i] == B[j]; j++) ;
    if(!ls.count(B[i])) {
      cout << -1 << endl;
      exit(0);
    }
    ret += max(ls[B[i]] - i, 0);
    ret += max(j - rs[B[i]], 0);
  }
  cout << ret << endl;
}
