#include <bits/stdc++.h>

using namespace std;

vector<pair<int, int>> split(const vector<pair<int, int>> &v, const vector<int> &pos)
{
	vector<pair<int, int>> ret;
	for(auto[l, r] : v)
	{
		if(l == r)
		{
			ret.emplace_back(l, r);
			continue;
		}
		int last = l;
		auto it = upper_bound(pos.begin(), pos.end(), l);
		while(it != pos.end() && (*it) <= r)
		{
			ret.emplace_back(last, *it);
			last = *it;
			it++;
		}
	}
	return ret;
}

long double f(int l1, int r1, int l2, int r2)
{
	if(l1 == l2 && r1 == r2)
	{
		return (r1 - l1) / 3.0L;
	}
	if(r1 <= l2 || r2 <= l1)
	{
		long double E1 = (l1 + r1) / 2.0L;
		long double E2 = (l2 + r2) / 2.0L;
		return abs(E1 - E2);
	}
	return 0;
}

int main()
{
	ios_base::sync_with_stdio(false), cin.tie(NULL);
	int n, m;
	cin >> n >> m;
	vector<pair<int, int>> a(n), b(m);
	int tota = 0, totb = 0;
	for(int i = 0; i < n; ++i)
	{
		cin >> a[i].first >> a[i].second;
		tota += (a[i].second - a[i].first);
	}
	for(int i = 0; i < m; ++i)
	{
		cin >> b[i].first >> b[i].second;
		totb += (b[i].second - b[i].first);
	}
	vector<int> pos;
	for(auto[l, r] : a)
		pos.push_back(l), pos.push_back(r);
	for(auto[l, r] : b)
		pos.push_back(l), pos.push_back(r);
	sort(pos.begin(), pos.end());
	pos.erase(unique(pos.begin(), pos.end()), pos.end());

	a = split(a, pos);
	b = split(b, pos);
	n = a.size();
	m = b.size();

	sort(a.begin(), a.end());
	sort(b.begin(), b.end());
	
	vector<long long> pref_prob(m), pref_exp(m);
	for(int i = 0; i < m; ++i)
	{
		auto [l2, r2] = b[i];
		long long E2 = (l2 + r2);
		long long prob2 = 1;
		if(totb)
			prob2 = (r2 - l2);
		if(i == 0)
		{
			pref_prob[i] = prob2;
			pref_exp[i] = E2 * prob2;
		}
		else
		{
			pref_prob[i] = pref_prob[i - 1] + prob2;
			pref_exp[i] = pref_exp[i - 1] + E2 * prob2;
		}
	}

	long double ans = 0;
	for(int i = 0; i < n; ++i)
	{
		auto [l1, r1] = a[i];
		long double prob1 = 1.0L / n;
		long long E1 = (l1 + r1);
		if(tota)
			prob1 = (r1 - l1) * 1.0L / tota;
		int jj = lower_bound(b.begin(), b.end(), make_pair(l1, -1)) - b.begin();
		if(jj > 0)
			ans += prob1 * (pref_prob[jj - 1] * E1 - pref_exp[jj - 1]) / 2.0L;
		for(int j = jj; j < m; ++j)
		{
			auto [l2, r2] = b[j];
			long long prob2 = 1;
			if(totb)
				prob2 = (r2 - l2);
			ans += prob1 * prob2 * f(l1, r1, l2, r2);
		}
	}

	if(totb)
		ans /= totb;
	else
		ans /= m;

	cout << setprecision(20) << fixed << ans << endl;
}