#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <queue>
#include <map>
#include <set>
#include <cmath>
#include <sstream>
#include <cstring>

#define pb push_back
#define mp make_pair
#define PI 3.14159265358979
#define sqr(x) (x)*(x)
#define forn(i, n) for(int i = 0; i < n; ++i)
#define ALL(x) x.begin(), x.end()
#define sz(x) int((x).size())
#define X first
#define Y second
typedef long long ll;
typedef long double ld;
using namespace std;
typedef pair<int,int> pii;
const int INF = 2147483647;
const ll LLINF = 9223372036854775807LL;
const int maxn = 310;
const int maxt = 1010;
int xx[maxn], yy[maxn];
int mx[maxt], my[maxt];
double d[maxn][maxn] = {};
bool good[maxn][maxn] = {};
int main()
{
#ifndef ONLINE_JUDGE
    freopen("mines.in", "r", stdin);
    freopen("mines.out", "w", stdout);
#endif
    int n, k; scanf("%d%d", &n, &k);
    memset(good, 0, sizeof(good));
    for (int i = 0; i < n; ++i) scanf("%d%d", &xx[i], &yy[i]);
    for (int i = 0; i < k; ++i) scanf("%d%d", &mx[i], &my[i]);
    const double cinf = 1e10;
    for (int i = 0; i < n; ++i) for (int j = 0; j < n; ++j) d[i][j] = cinf*(i!=j);
    double best = cinf;
    for (int i = 0; i < n; ++i)
        for (int j = i+1; j < n; ++j) {
            bool ok = true;
            for (int t = 0; t < k; ++t) {
                int vx = xx[j]-xx[i];
                int vy = yy[j]-yy[i];
                int tx = mx[t]-xx[i];
                int ty = my[t]-yy[i];
                int cur = vx*ty-vy*tx;
                if (cur != 0) ok = false;
                if (!(vx*tx+vy*ty>=0 && -vx*(mx[t]-xx[j])-vy*(my[t]-yy[j])>=0)) ok = false;
            }
            double curd = sqrt(0.+sqr(xx[i]-xx[j])+sqr(yy[i]-yy[j]));
            if (ok) best = min(best, 2*curd);
        }
    for (int i = 0; i < n; ++i)
        for (int j = i+1; j < n; ++j) {
            bool haspos = false;
            bool hasneg = false;
            for (int t = 0; t < k; ++t) {
                int vx = xx[j]-xx[i];
                int vy = yy[j]-yy[i];
                int tx = mx[t]-xx[i];
                int ty = my[t]-yy[i];
                int cur = vx*ty-vy*tx;
                if (cur > 0) haspos = true;
                if (cur < 0) hasneg = true;
            }
            if (haspos && hasneg) continue;
            double curd = sqrt(0.+sqr(xx[i]-xx[j])+sqr(yy[i]-yy[j]));
            if (haspos) d[i][j] = curd, good[i][j] = 1;
            if (hasneg) d[j][i] = curd, good[j][i] = 1;
        }
    for (int t = 0; t < n; ++t)
        for (int i = 0; i < n; ++i)
            for (int j = 0; j < n; ++j) {
                if (d[i][j] > d[i][t]+d[t][j]) {
                    d[i][j] = d[i][t]+d[t][j];
                }
            }

    for (int i = 0; i < n; ++i)
        for (int j = 0; j < n; ++j) {
            if (good[i][j]) {
                best = min(best, d[i][j]+d[j][i]);
            }
        }
    if (best < cinf) printf("%.10lf\n", best);
    else printf("-1\n");
    return 0;
}