#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#define ff first
#define ss second
using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

typedef long double ld;
const ld eps = 1e-9;

struct point {
	ld x, y;
};
point operator+(point a, point b) { return {a.x + b.x, a.y + b.y}; }
point operator-(point a, point b) { return {a.x - b.x, a.y - b.y}; }
ld operator*(point a, point b) { return a.x * b.x + a.y * b.y; }
ld operator/(point a, point b) { return a.x * b.y - a.y * b.x; }
point operator*(ld k, point a) { return {k * a.x, k * a.y}; }
ld dst(point a, point b) { return sqrt((a - b) * (a - b)); }
point unit(point a) { return 1 / sqrt(a * a) * a; }

mt19937 rnd(1557);
int rng(int l, int r) {
	return uniform_int_distribution<int>(l, r)(rnd);
}

int main() {
	cin.tie(0); ios_base::sync_with_stdio(0);
	int n;
	cin >> n;
	point x[n]; ld d[n]{};
	// for (int i = 0; i < n; i++) {
	// 	x[i].x = rng(-30000, 30000);
	// 	x[i].y = rng(-30000, 30000);
	// }
	for (int i = 0; i < n; i++) cin >> x[i].x >> x[i].y;
	for (int i = 1; i < n; i++) d[i] = d[i - 1] + dst(x[i], x[i - 1]);
	int m;
	cin >> m;
	point y[m]; ld e[m]{};
	// for (int i = 0; i < m; i++) {
	// 	y[i].x = rng(-30000, 30000);
	// 	y[i].y = rng(-30000, 30000);
	// }
	for (int i = 0; i < m; i++) cin >> y[i].x >> y[i].y;
	for (int i = 1; i < m; i++) e[i] = e[i - 1] + dst(y[i], y[i - 1]);
	if (dst(x[0], y[m - 1]) > e[m - 1] + eps) {
		return !(cout << "impossible\n");
	}
	int p = 0, q = 0;
	while (q < m - 1 && dst(x[0], y[q + 1]) > e[q + 1]) ++q;
	ld prv = 0;
	ld ans = 1e9;
	while (p != n - 1 && q != m - 1) {
		point vecx = unit(x[p + 1] - x[p]);
		point vecy = unit(y[q + 1] - y[q]);
		auto get = [&](ld t) {
			point sec = x[p] + (t - d[p]) * vecx - y[q] + e[q] * vecy;
			if (abs(sec * vecy - t) < eps) return e[q];
			else return (t * t - sec * sec) / (2 * (t - sec * vecy));
		};
		if (d[p + 1] + dst(x[p + 1], y[q + 1]) < e[q + 1]) {
			ld ss = prv, ee = d[p + 1];
			// ternary search
			for (int it = 0; it < 100; it++) {
				ld mid1 = (2 * ss + ee) / 3;
				ld mid2 = (ss + 2 * ee) / 3;
				ld k1 = get(mid1);
				ld k2 = get(mid2);
				point P1 = x[p] + (mid1 - d[p]) * vecx;
				point P2 = x[p] + (mid2 - d[p]) * vecx;
				point Q1 = y[q] + (k1 - e[q]) * vecy;
				point Q2 = y[q] + (k2 - e[q]) * vecy;
				ld d1 = dst(P1, Q1);
				ld d2 = dst(P2, Q2);
				ans = min(ans, min(d1, d2));
				if (d1 > d2) {
					ss = mid1;
				}
				else {
					ee = mid2;
				}
			}
			prv = d[p + 1];
			++p;
		}
		else {
			ld cur;
			{
				ld ss = d[p], ee = d[p + 1];
				for (int it = 0; it < 60; it++) {
					ld mid = (ss + ee) / 2;
					point P = x[p] + (mid - d[p]) * vecx;
					if (dst(P, y[q + 1]) > e[q + 1] - mid + eps) ee = mid;
					else ss = mid;
				}
				cur = ss;
			}
			ld ss = prv, ee = cur;
			// ternary search
			for (int it = 0; it < 100; it++) {
				ld mid1 = (2 * ss + ee) / 3;
				ld mid2 = (ss + 2 * ee) / 3;
				ld k1 = get(mid1);
				ld k2 = get(mid2);
				point P1 = x[p] + (mid1 - d[p]) * vecx;
				point P2 = x[p] + (mid2 - d[p]) * vecx;
				point Q1 = y[q] + (k1 - e[q]) * vecy;
				point Q2 = y[q] + (k2 - e[q]) * vecy;
				ld d1 = dst(P1, Q1);
				ld d2 = dst(P2, Q2);
				ans = min(ans, min(d1, d2));
				if (d1 > d2) {
					ss = mid1;
				}
				else {
					ee = mid2;
				}
			}
			prv = cur;
			++q;
		}
	}
	cout.precision(10);
	cout << fixed << ans << '\n';
}