func_code_string: #include <bits/stdc++.h>   using namespace std;   const int N = 1010;   struct Point {     double x, y;     Point(double _ = 0, double __ = 0) { x = _, y = __; }     bool operator<(const Point &_) const {       if (fabs(x - _.x) > 1e-10) return x < _.x;       return y < _.y;     }   } po[N], rec[N * 2], stk[N * 2];   struct Line {     Point a, b;   } L;   struct Mem {     Point a;     int type;     bool operator<(const Mem &_) const {       if (fabs(a.x - _.a.x) > 1e-10) return a.x < _.a.x;       if (fabs(a.y - _.a.y) > 1e-10) return a.y < _.a.y;       return type < _.type;     }   } pp[N * 2];   int n, m;   inline double xmul(Point a, Point b, Point c) {     return (a.x - b.x) * (a.y - c.y) - (a.y - b.y) * (a.x - c.x);   }   inline bool across(Point &a, Point &b, Point &c, Point &d) {     double p1 = xmul(a, b, c), p2 = xmul(a, b, d);     if (fabs(p1) < 1e-10 || fabs(p2) < 1e-10) return 1;     if (p1 * p2 < 1e-10) return 1;     return 0;   }   inline bool oneline(Point &a, Point &b, Point &c, Point &d) {     double p1 = xmul(a, b, c), p2 = xmul(a, b, d);     if (fabs(p1) < 1e-10 && fabs(p2) < 1e-10) return 1;     return 0;   }   inline Point intersection(Line &u, Line &v) {     Point ret = u.a;     double t =         ((u.a.x - v.a.x) * (v.a.y - v.b.y) - (u.a.y - v.a.y) * (v.a.x - v.b.x)) /         ((u.a.x - u.b.x) * (v.a.y - v.b.y) - (u.a.y - u.b.y) * (v.a.x - v.b.x));     ret.x += (u.b.x - u.a.x) * t;     ret.y += (u.b.y - u.a.y) * t;     return ret;   }   inline double dis(Point &a, Point &b) {     return sqrt(((a.x - b.x) * (a.x - b.x)) + ((a.y - b.y) * (a.y - b.y)));   }   inline bool onseg(Point &a, Point &b, Point &c) {     if (fabs(xmul(a, b, c)) < 1e-10) return 1;     return 0;   }   inline double getans() {     Point a, b;     int tot = 0, cnt = 0, top = 0;     double ans = 0;     for (int i = 1; i <= n; i++) {       if (oneline(L.a, L.b, po[i], po[i + 1])) {         cnt++;         pp[cnt].a = po[i];         pp[cnt].type = 1;         cnt++;         pp[cnt].a = po[i + 1];         pp[cnt].type = -1;         if (pp[cnt].a < pp[cnt - 1].a) swap(pp[cnt].a, pp[cnt - 1].a);         continue;       }       int k1 = onseg(L.a, L.b, po[i]) || xmul(L.a, L.b, po[i]) < 0;       int k2 = onseg(L.a, L.b, po[i + 1]) || xmul(L.a, L.b, po[i + 1]) < 0;       if (k1 + k2 != 1) continue;       if (onseg(L.a, L.b, po[i])) {         rec[++tot] = po[i];         continue;       }       if (onseg(L.a, L.b, po[i + 1])) {         rec[++tot] = po[i + 1];         continue;       }       if (across(L.a, L.b, po[i], po[i + 1])) {         Line tmp;         tmp.a = po[i], tmp.b = po[i + 1];         rec[++tot] = intersection(L, tmp);       }     }     sort(rec + 1, rec + tot + 1);     for (int i = 1; i < tot; i += 2) {       cnt++;       pp[cnt].a = rec[i];       pp[cnt].type = 1;       cnt++;       pp[cnt].a = rec[i + 1];       pp[cnt].type = -1;     }     sort(pp + 1, pp + cnt + 1);     for (int i = 1; i <= cnt; i++) {       if (pp[i].type == 1)         stk[++top] = pp[i].a;       else {         if (top == 1) ans += dis(stk[top], pp[i].a);         top--;       }     }     return ans;   }   int main() {     scanf( %d %d , &n, &m);     for (int i = 1; i <= n; i++) scanf( %lf%lf , &po[i].x, &po[i].y);     po[n + 1] = po[1];     for (int i = 1; i <= m; i++) {       scanf( %lf%lf%lf%lf , &L.a.x, &L.a.y, &L.b.x, &L.b.y);       printf( %.8lf n , getans());     }     return 0;   }   