P1041 传染病控制

#include <bits/stdc++.h>
using namespace std;
const int maxn = 301;
std::vector<int> son[maxn];
vector<int> G[maxn];
int deep[maxn], size[maxn];
vector<int> dep[maxn];
int vis[maxn];
int n, p, ans = 0x3f3f3f;
inline void dfs(int f) {
  vector<int>::iterator it;
  size[f] = 1;
  for (it = son[f].begin(); it != son[f].end(); it++) {
    int x = *it;
    deep[x] = deep[f] + 1;
    dfs(x);
    size[f] += size[*it];
  }
}
inline void hit(int root, int state) {
  vector<int>::iterator it;
  if (state == 1)
    vis[root] = 1;
  else
    vis[root] = 0;
  for (it = son[root].begin(); it != son[root].end(); it++) {
    hit(*it, state);
  }
}
inline void search(int d, int now) {
  ans = min(ans, now);
  vector<int>::iterator it;
  for (it = dep[d].begin(); it != dep[d].end(); it++) {
    if (!vis[*it]) {
      hit(*it, 1);
      search(d + 1, now - size[*it]);
      hit(*it, 0);
    }
  }
}
int v[maxn];
inline void trans(int root) {
  v[root] = 1;
  vector<int>::iterator it;
  for (it = G[root].begin(); it != G[root].end(); it++) {
    if (!v[*it]) {
      son[root].push_back(*it);
      trans(*it);
    }
  }
}
inline int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-')
      f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
int main() {
//  freopen("input.in", "r", stdin);
  cin >> n >> p;
  for (int i = 1; i <= p; i++) {
    int x, y;
    x = read();
    y = read();
    G[x].push_back(y);
    G[y].push_back(x);
  }
  memset(v, 0, sizeof(v));
  trans(1);
  deep[1] = 0;
  dfs(1);
  for (int i = 1; i <= n; i++) {
    dep[deep[i]].push_back(i);
  }
  search(1, n);
  printf("%d\n", ans);
  return 0;
}