1 #include <iostream>
  2 #include <math.h>
  3 #include <stdio.h>
  4 #include <algorithm>
  5 #include <string.h>
  6 
  7 using namespace std;
  8 
  9 const int MAXN = 100005;
 10 int first[MAXN], n, m, en, color[MAXN], f[2], u, v; //f统计不同颜色节点数 
 11 int front, rear; 
 12 bool vis[MAXN]; 
 13 int ans;
 14 
 15 struct edge
 16 {
 17     int zhongdian, changdu;
 18     int next;
 19 };
 20 
 21 edge ed[MAXN]; 
 22 
 23 void add_edge(int s, int e, int d) 
 24 {
 25     en++; 
 26     ed[en].next = first[s]; 
 27     first[s] = en;
 28     ed[en].zhongdian = e;
 29     ed[en].changdu = d;
 30 }
 31 
 32 struct Node
 33 {
 34     int x, y;
 35     int step;
 36 };
 37 Node q[MAXN];
 38 
 39 int bfs(int a)
 40 {
 41     Node now, next;
 42     now.x = a;
 43     vis[a] = 1;
 44     color[a] = 1;
 45     f[0] = 0;
 46     f[1] = 1;
 47     front = rear = 0;
 48     q[rear] = now;
 49     rear++;
 50     while(front < rear)
 51     {
 52         now = q[front++];
 53         for(int i = first[now.x]; i; i = ed[i].next)
 54         //first[now]：当前点的第一条边；ed[i].next：下一个访问的点  
 55         {
 56             if(color[ed[i].zhongdian] != -1)
 57             {
 58                 if(color[ed[i].zhongdian] == color[now.x])
 59                 {
 60                     cout << "Impossible" << endl;
 61                     return -1;
 62                 }
 63             } 
 64             else
 65             {
 66                 color[ed[i].zhongdian] = (color[now.x] + 1) % 2;
 67                 q[rear].x = ed[i].zhongdian;
 68                 rear++;
 69                 f[color[ed[i].zhongdian]]++;
 70             }
 71         } 
 72     }
 73     ans += min(f[0], f[1]);
 74 }
 75 
 76 int main()
 77 {
 78     cin >> n >> m;
 79     for(int i = 1; i <= n; i++)
 80     {
 81         color[i] = -1; //初始化  
 82     }
 83     for(int i = 1; i <= m; i++)
 84     {
 85         cin >> u >> v;
 86         add_edge(u, v, 0);
 87         add_edge(v, u, 0);
 88     }
 89     for(int i = 1; i <= n; i++)
 90     {
 91         if(color[i] == -1)
 92         {
 93             if(bfs(i) < 0)
 94             {
 95                 return 0;
 96             }
 97         } 
 98     }
 99     cout << ans << endl;
100     
101     return 0;
102 }