func_code_string: #include <bits/stdc++.h>   using namespace std;   const int N = 100100, M = 200200;   int i, j, k, n, q, m, nm, ch, ii;   int l[N], r[N], fg[N];   struct cc {     int x, y;   } t, A[M], P[M];   void R(int &x) {     x = 0;     ch = getchar();     while (ch <  0  ||  9  < ch) ch = getchar();     while ( 0  <= ch && ch <=  9 ) x = x * 10 + ch -  0 , ch = getchar();   }   void W(int x) {     if (x >= 10) W(x / 10);     putchar(x % 10 +  0 );   }   long long dis(const cc &a, const cc &b) {     return (long long)(a.x - b.x) * (a.x - b.x) +            (long long)(a.y - b.y) * (a.y - b.y);   }   bool cmp1(const cc &a, const cc &b) {     if (a.x == b.x) return a.y < b.y;     return a.x < b.x;   }   bool cmp2(const cc &a, const cc &b) {     int x1, y1, x2, y2;     x1 = a.x - A[1].x;     y1 = a.y - A[1].y;     x2 = b.x - a.x;     y2 = b.y - a.y;     if ((long long)x1 * y2 == (long long)x2 * y1)       return dis(A[1], a) < dis(A[1], b);     return (long long)x1 * y2 < (long long)x2 * y1;   }   bool check(const cc &a, const cc &b, const cc &c) {     int x1, y1, x2, y2;     x1 = b.x - a.x;     y1 = b.y - a.y;     x2 = c.x - b.x;     y2 = c.y - b.y;     if ((long long)x1 * y2 == (long long)x2 * y1) return dis(a, b) < dis(a, c);     return (long long)x1 * y2 > (long long)x2 * y1;   }   bool check2(const cc &a, const cc &b, const cc &c) {     int x1, y1, x2, y2;     x1 = b.x - a.x;     y1 = b.y - a.y;     x2 = c.x - b.x;     y2 = c.y - b.y;     return (long long)x1 * y2 < (long long)x2 * y1;   }   bool find(int x, int y) {     if (fg[x] != ii) return 0;     if (y < l[x] || r[x] < y) return 0;     return 1;   }   int main() {     R(n);     R(q);     while (n && q) {       ii++;       m = 0;       for (i = 1; i <= q; i++) {         R(P[i].x);         R(P[i].y);         if (fg[P[i].x] != ii) {           fg[P[i].x] = ii;           l[P[i].x] = r[P[i].x] = P[i].y;         } else {           l[P[i].x] = ((l[P[i].x]) < (P[i].y) ? (l[P[i].x]) : (P[i].y));           r[P[i].x] = ((r[P[i].x]) < (P[i].y) ? (P[i].y) : (r[P[i].x]));         }       }       for (k = 1; k <= q; k++) {         i = P[k].x;         j = P[k].y;         if (!find(i + 1, j - 1) && !find(i + 1, j) && !find(i, j - 1))           A[++m].x = i - 1, A[m].y = j;         if (!find(i + 1, j + 1) && !find(i + 1, j) && !find(i, j + 1))           A[++m].x = i - 1, A[m].y = j - 1;         if (!find(i - 1, j + 1) && !find(i - 1, j) && !find(i, j + 1))           A[++m].x = i, A[m].y = j - 1;         if (!find(i - 1, j - 1) && !find(i - 1, j) && !find(i, j - 1))           A[++m].x = i, A[m].y = j;       }       sort(A + 1, A + m + 1, cmp1);       A[m + 1].x = -1;       nm = 0;       for (i = 1; i <= m; i++)         if (A[i].x != A[i + 1].x || A[i].y != A[i + 1].y) A[++nm] = A[i];       sort(A + 2, A + nm + 1, cmp2);       m = 2;       for (i = 3; i <= nm; i++) {         while (m >= 2 && check(A[m - 1], A[m], A[i])) m--;         if (m < 2)           A[++m] = A[i];         else if (check2(A[m - 1], A[m], A[i]))           A[++m] = A[i];       }       while (m >= 2 && check(A[m - 1], A[m], A[1])) m--;       W(m);       puts(  );       for (i = 1; i <= m; i++) W(A[i].x), putchar(   ), W(A[i].y), puts(  );       R(n);       R(q);     }   }   