排不出错，交上去wa，求神犇看看

#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<queue>
#include<set>
using namespace std;
typedef long long LL;
#define N 100010
struct edge
{
    int to,next,w;
}e[N<<2];
int head[N];
int cnt;
int col[N];
int n,m;
void link(int x,int y)
{
    e[++cnt]=(edge){y,head[x]};
    head[x]=cnt;
}
bool dfs(int x)
{
    for (int i=head[x],y;i,y=e[i].to;i=e[i].next)
    {
        if (!col[y])
        {
            col[y]=!col[x];
            if (!dfs(y))
                return 0;
        }
        else if (col[x]==col[y])
            return 0;
    }
    return 1;
}
int main()
{
    freopen("a.in","r",stdin);freopen("a.out","w",stdout);
    scanf("%d%d",&n,&m);
    for (int i=1,x,y;i<=m;i++)
    {
        scanf("%d%d",&x,&y);
        link(x,y);
        link(y,x);
    }
    for (int i=1;i<=n;i++)
        if (!dfs(i))
        {
            printf("Impossible\n");
            return 0;
        }
    int ans=0;
    for (int i=1;i<=n;i++)
        if (!col[i])
            ans++;
    printf("%d",min(ans,n-ans));
    return 0;
}