Точность попадания снаряда

#define _USE_MATH_DEFINES
#include <iostream>
#include <string>
#include <map>
#include <set>
#include <algorithm>
#include <vector>
#include <stdio.h>
#include <cmath>
#include <math.h>
#include <queue>
#include <stack>
#include <climits>
#include <deque>
#include <ctime>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int ui;

#define mh() make_heap()
#define poph() pop_heap()
#define pushh() push_heap()
#define sor(n) n.begin(), n.end()
#define rsor(n) n.rbegin(), n.rend()
#define mp make_pair
#define files freopen("input.txt", "rt", stdin); freopen("output.txt", "wt", stdout)
#define p(T) pair<T,T>
#define znac(l) abs(l)/l

#define A(y1,y2) y1-y2
#define B(x1,x2) x2-x1
#define C(x1,y1,x2,y2) -y2*(x2-x1)-x2*(y1-y2)

#define rs(x1,y1,x2,y2) sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1))

struct pt {
    double x, y;
};

struct line {
    double a, b, c;
};

const double EPS = 1e-9;

double det(double a, double b, double c, double d) {
    return a * d - b * c;
}

bool intersect(line m, line n, pt & res) {
    double zn = det(m.a, m.b, n.a, n.b);
    if (abs(zn) < EPS)
        return false;
    res.x = -det(m.c, m.b, n.c, n.b) / zn;
    res.y = -det(m.a, m.c, n.a, n.c) / zn;
    return true;
}

bool parallel(line m, line n) {
    return abs(det(m.a, m.b, n.a, n.b)) < EPS;
}

bool equivalent(line m, line n) {
    return abs(det(m.a, m.b, n.a, n.b)) < EPS
        && abs(det(m.a, m.c, n.a, n.c)) < EPS
        && abs(det(m.b, m.c, n.b, n.c)) < EPS;
}

double MIN(p(double)fr, p(double)sc, p(double)t)
{
    line frst = { A(fr.second,sc.second),B(fr.first,sc.first),C(fr.first,fr.second,sc.first,sc.second) };
    line sec = {-frst.b,frst.a,frst.b*t.first-frst.a*t.second };
    if (!parallel(frst, sec) && !equivalent(frst, sec))
    {
        pt res;
        intersect(frst, sec, res);
        double l = rs(fr.first, fr.second, sc.first, sc.second);
        double ll = rs(fr.first, fr.second, res.x, res.y);
        double lr = rs(res.x, res.y, sc.first, sc.second);
        if (abs(l-(ll + lr)) > EPS)
        {
            return min(rs(fr.first, fr.second, t.first, t.second), rs(t.first, t.second, sc.first, sc.second));
        }
        else
        {
            double H = abs((frst.a*t.first +frst.b*t.second + frst.c) / sqrt(frst.a*frst.a + frst.b*frst.b));
            return min(H, min(rs(fr.first, fr.second, t.first, t.second), rs(t.first, t.second, sc.first, sc.second)));
        }
    }
    else
    {
        return min(rs(fr.first, fr.second, t.first, t.second), rs(t.first, t.second, sc.first, sc.second));
    }
}

int main()
{
#ifndef ONLINE_JUDGE
    files;
#endif

    p(double) t;
    ll n;

    cin >> t.first >> t.second>>n;
    vector<p(double)>cord(n + 1);
    for (int i = 1; i <= n; i++)
    {
        cin >> cord[i].first >> cord[i].second;
    }
    ll last = 0;
    bool good = 1;
    for (int i = 1; i <= n; i++)
    {
        double ras;
        line frst;
        if (i == 1)
        {
            frst = { A(cord[i].second,cord[n].second),B(cord[i].first,cord[n].first),C(cord[i].first,cord[i].second,cord[n].first,cord[n].second) };
        }
        else
            frst = { A(cord[i].second,cord[i-1].second),B(cord[i].first,cord[i-1].first),C(cord[i].first,cord[i].second,cord[i-1].first,cord[i-1].second) };
        double H = (frst.a*t.first + frst.b*t.second + frst.c) / sqrt(frst.a*frst.a + frst.b*frst.b);
        if (last == 0)
        {
            last = znac(H);
        }
        else
        {
            if (abs(H) < EPS)
            {
            }
            else
                if (last != znac(H))
                {
                    good = 0;
                    break;
                }
        }
    }
    if (good)
    {
        printf("%.3lf", 0.0);
        return 0;
    }
    double answ = INT_MAX;
    for (int i = 1; i <= n; i++)
    {
        double ras;
        if (i == 1)
        {
            ras = MIN(cord[i], cord[n], t);
        }
        else
        {
            ras = MIN(cord[i], cord[i-1], t);
        }
        answ = min(answ, ras);
    }
    printf("%.3lf", 2*answ);
    return 0;
}