////////////////////////////////////////
///  tu3 pro-con template            ///
////////////////////////////////////////
#include <cassert>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <iostream>
#include <sstream>
#include <algorithm>
#include <numeric>
#include <functional>
#include <vector>
#include <queue>
#include <string>
#include <complex>
#include <stack>
#include <set>
#include <map>
#include <list>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <regex>
using namespace std;

//// MACRO ////
#define countof(a) (sizeof(a)/sizeof(a[0]))

#define REP(i,n) for (int i = 0; i < (n); i++)
#define RREP(i,n) for (int i = (n)-1; i >= 0; i--)
#define FOR(i,s,n) for (int i = (s); i < (n); i++)
#define RFOR(i,s,n) for (int i = (n)-1; i >= (s); i--)
#define pos(c,i) c.being() + (i)
#define allof(c) c.begin(), c.end()
#define aallof(a) a, countof(a)
#define partof(c,i,n) c.begin() + (i), c.begin() + (i) + (n)
#define apartof(a,i,n) a + (i), a + (i) + (n)
#define long long long

#define EPS 1e-9
#define INF (1L << 30)
#define LINF (1LL << 60)

#define PREDICATE(t,a) (const t & a) -> bool
#define COMPARISON_T(t) bool(*)(const t &, const t &)
#define COMPARISON(t,a,b) (const t & a, const t & b) -> bool
#define CONVERTER(TSrc,t,TDest) (const TSrc &t)->TDest

//// i/o helper ////

struct _Reader { template <class T> _Reader operator ,(T &rhs) { cin >> rhs; return *this; } };
struct _Writer { bool f; _Writer() : f(false) { } template <class T> _Writer operator ,(const T &rhs) { cout << (f ? " " : "") << rhs; f = true; return *this; } };
#define READ(t,...) t __VA_ARGS__; _Reader(), __VA_ARGS__
#define WRITE(...) _Writer(), __VA_ARGS__; cout << endl
inline int sign(double x) { return (abs(x) < EPS ? 0 : x > 0 ? 1 : -1); }

template <class T> struct vevector : public vector<vector<T>> { vevector(int n = 0, int m = 0, const T &initial = T()) : vector<vector<T>>(n, vector<T>(m, initial)) { } };
template <class T> struct vevevector : public vector<vevector<T>> { vevevector(int n = 0, int m = 0, int l = 0, const T &initial = T()) : vector<vevector<T>>(n, vevector<T>(m, l, initial)) { } };
template <class T> struct vevevevector : public vector<vevevector<T>> { vevevevector(int n = 0, int m = 0, int l = 0, int k = 0, const T &initial = T()) : vector<vevevector<T>>(n, vevevector<T>(m, l, k, initial)) { } };
template <class T> T read() { T t; cin >> t; return t; }
template <class T> vector<T> read(int n) { vector<T> v; REP(i, n) { v.push_back(read<T>()); } return v; }
template <class T> vevector<T> read(int n, int m) { vevector<T> v; REP(i, n) v.push_back(read<T>(m)); return v; }
template <class T> vevector<T> readjag() { return read<T>(read<int>()); }
template <class T> vevector<T> readjag(int n) { vevector<T> v; REP(i, n) v.push_back(readjag<T>()); return v; }

template <class T1, class T2> inline istream & operator >> (istream & in, pair<T1, T2> &p) { in >> p.first >> p.second; return in; }
template <class T1, class T2> inline ostream & operator << (ostream &out, pair<T1, T2> &p) { out << p.first << p.second; return out; }
template <class T> inline ostream & operator << (ostream &out, vector<T> &v)
{
	ostringstream ss;
	for (auto x : v) ss << x << ' ';
	auto s = ss.str();
	out << s.substr(0, s.length() - 1) << endl;
	return out;
}

//// start up ////
void solve();
int main()
{
	solve();
	return 0;
}
//// geometry ////

/// 2次元
struct P2
{
	double x, y;
	P2(double x = 0, double y = 0) : x(x), y(y) { }
	P2(complex<double> c) : x(c.real()), y(c.imag()) { }
	P2 operator +() const { return *this; }
	P2 operator +(const P2 &_) const { return P2(x + _.x, y + _.y); }
	P2 operator -() const { return P2(-x, -y); }
	P2 operator -(const P2 &_) const { return *this + -_; }
	P2 operator *(double _) const { return P2(x*_, y*_); }
	P2 operator /(double _) const { return P2(x / _, y / _); }
	double dot(const P2 &_) const { return x*_.x + y*_.y; } // 内積
	double cross(const P2 &_) const { return x*_.y - y*_.x; } // 外積
	double sqlength() const { return x*x + y*y; } // 二乗長さ
	double length() const { return sqrt(sqlength()); } // 長さ
	P2 orthogonal() const { return P2(y, -x); }
	P2 direction() const { return *this / length(); } // 方向ベクトル
};
inline istream & operator>>(istream & in, P2 & p) { in >> p.x >> p.y; return in; }
inline ostream & operator<<(ostream & out, const P2 & p) { out << p.x << ' ' << p.y; return out; }
inline double abs(P2 p2) { return p2.length(); }
inline P2 orthogonal(P2 p) { return p.orthogonal(); }
inline complex<double> orthogonal(complex<double> c) { return  c * complex<double>(0, 1); }

// a,b から ちょうど d だけ離れた点。aとbを円周に持つ円の半径。
inline pair<P2, P2> get_same_distance_points(P2 a, P2 b, double d)
{
	assert(abs(a - b) <= 2 * d + EPS);
	auto v = (a + b) / 2.0 - a; // a から aとbの中点
	auto vl = abs(v);
	auto wl = sqrt(d*d - vl*vl); // 直行Vの大きさ
	auto w = orthogonal(v) * (wl / vl); // 直行V
	return make_pair(a + v + w, a + v - w);
}


struct Circle
{
	P2 c;
	double r;
	Circle() : c(), r() { }
	Circle(double x, double y, double r) : c(x, y), r(r) { }
	Circle(P2 c, double r) : c(c), r(r) { }
	bool IntersectWith(const Circle &rhs) const { return abs(c - rhs.c) - (r + rhs.r) < EPS; } // 接してても真。
	bool Contains(const P2 &p) const { return abs(p - c) - r < EPS; } // 接してても真。
};
inline istream & operator>>(istream & in, Circle & c) { in >> c.c >> c.r; return in; }

// 交差している2円の交点を求める。角度の小さい方から出る(右下方向が正なら時計回り)
inline pair<P2, P2> crossPoint(Circle A, Circle B)
{
	P2 v = B.c - A.c;
	P2 dir = v.direction(); // 他方の中心への方向
	double d = v.length(); // 他方の中心への距離
	double lh = (A.r*A.r + d*d - B.r*B.r) / (2 * d); // 垂線の足までの距離
	P2 h = A.c + dir * lh; // 垂線の足
	double lp = sqrt(A.r*A.r - lh*lh); // 垂線の足から交点までの距離
	P2 p = dir.orthogonal() * lp; // 垂線の足から交点へのベクトル
	return make_pair(h + p, h - p); // 交点の組。
}

inline int clockwise(P2 a, P2 b, P2 c)
{
	const P2 u = b - a, v = c - a;
	if (u.cross(v) > EPS) { return 1; }
	if (u.cross(v) < -EPS) { return -1; }
	if (u.dot(v) < -EPS) { return -1; }
	if (abs(u) - abs(v) < EPS) { return 1; }
	return 0;
}

struct Line
{
	P2 p, d;
	explicit Line(P2 pos = P2(), P2 dir = P2()) : p(pos), d(dir) { }
	static Line FromPD(P2 pos, P2 dir) { return Line(pos, dir); }
	static Line From2Point(P2 a, P2 b) { return Line(a, b - a); }
};

struct LineSeg
{
	P2 p, d;
	explicit LineSeg(P2 pos = P2(), P2 dir = P2()) : p(pos), d(dir) { }
	static LineSeg FromPD(P2 pos, P2 dir) { return LineSeg(pos, dir); }
	static LineSeg From2Point(P2 a, P2 b) { return LineSeg(a, b - a); }
};


inline P2 crossPoint(Line a, Line b) { return a.p + a.d * (b.d.cross(b.p - a.p) / b.d.cross(a.d)); }
inline bool contains(LineSeg a, P2 p) { return abs(a.p - p) + abs(a.p + a.d - p) - abs(a.d) < EPS; }

inline bool isCross(Line a, Line b) { return abs(a.d.cross(b.d)) > EPS; }
inline bool isCross(Line a, LineSeg b) { return sign(a.d.cross(b.p - a.p)) * sign(a.d.cross(b.p + b.d - a.d)) <= 0; }
inline bool isCross(LineSeg a, Line b) { return isCross(b, a); }
inline bool isCross(LineSeg a, LineSeg b)
{
	P2 ae = a.p + a.d, be = b.p + b.d;
	return clockwise(a.p, ae, b.p) * clockwise(a.p, ae, be) <= 0
		&& clockwise(b.p, be, a.p) * clockwise(b.p, be, ae) <= 0;
}

inline bool isOverlap(Line a, Line b) { return abs(a.d.cross(b.p - a.p)) < EPS; }
inline bool isOverlap(Line a, LineSeg b) { return isOverlap(a, Line(b.p, b.d)); }
inline bool isOverlap(LineSeg a, Line b) { return isOverlap(b, a); }
inline bool isOverlap(LineSeg a, LineSeg b)
{
	return contains(a, b.p) || contains(a, b.p + b.d)
		|| contains(b, a.p) || contains(b, a.p + a.d);
}


//// graph ////

template <class TCost = double>
struct Path
{
	typedef TCost COST;
	int from;
	int to;
	TCost cost;
	Path(int from = 0, int to = 0, TCost cost = 0)
		: from(from), to(to), cost(cost) { }
	bool operator < (const Path &rhs) const { return cost < rhs.cost; }
	bool operator >(const Path &rhs) const { return cost > rhs.cost; }
};

// dijkstra //
template <class COST>
pair<vector<COST>, vector<int>> dijkstra(const vector<vector<Path<COST>>> &routes, int start = 0, int goal = -1)
{
	typedef Path<COST> P;
	int N = routes.size();
	priority_queue<P, vector<P>, greater<P>> q;
	q.push(P(start, start, 0));

	vector<int> prev(N, -1);
	vector<COST> cost(N, INF);
	while (!q.empty())
	{
		P cur = q.top(); q.pop();
		int i = cur.to;
		if (prev[i] != -1) continue;
		prev[i] = cur.from;
		cost[i] = cur.cost;
		if (i == goal) { break; }
		REP(j, routes[i].size())
		{
			P next = P(i, routes[i][j].to, cur.cost + routes[i][j].cost);
			if (prev[i] != -1)
				q.push(next);
		}
	}
	return make_pair(cost, prev);
}

////////////////////
/// template end ///
////////////////////

void solve()
{
	int testcases = 1;
	REP(testcase, testcases)
	{
		READ(int, Na, Nb);
		auto Pa = read<P2>(Na);
		auto Pb = read<P2>(Nb);
		LineSeg ASeg = LineSeg::From2Point(Pa[0], Pa[1]);
		LineSeg BSeg = LineSeg::From2Point(Pb[0], Pb[1]);

		if (!isCross(ASeg, BSeg))
		{
			printf("%.15f", ASeg.d.length() + BSeg.d.length());
		}
		else
		{
			vevector<Path<double> > Ga(Na);
			vevector<Path<double> > Gb(Nb);
			
			REP(i, Na) REP(j, Na)
			{
				LineSeg s = LineSeg::From2Point(Pa[i], Pa[j]);
				if (!isCross(BSeg, s)) Ga[i].push_back({ i, j, s.d.length() });
			}
			
			REP(i, Nb) REP(j, Nb)
			{
				LineSeg s = LineSeg::From2Point(Pb[i], Pb[j]);
				if (!isCross(ASeg, s)) Gb[i].push_back({ i, j, s.d.length() });
			}

			double aconn = ASeg.d.length() + dijkstra(Gb, 0, 1).first[1];
			double bconn = BSeg.d.length() + dijkstra(Ga, 0, 1).first[1];
			double ans = min(aconn, bconn);
			if (ans > INF) { WRITE(-1); }
			else { printf("%.15f", ans); }
		}
	}
}

Measured memory_bytes: 46500