//给一个无向图，其每个顶点都有权值，求去掉一条边，将这个图分为两部分
//问这两部分的所有顶点和的绝对值的最小值
//用tarjan缩点 ， 缩点后为一棵树
//然后用树形dp求出其最小的绝对值
// ans = min(ans , (int)(abs((double)(sum - 2*dp[v])))) ;
//其中dp[u] 表示以u点为根节点的子树的学生数
#include<cstdio>
#include<cstring>
#include<iostream>
#include<cmath>
#include<vector>
using namespace std ;
const int maxn = 10010 ;
const int maxm = 20010 ;
const int inf = 0x7fffffff ;
struct Edge
{
int v , u;
int next ;
}edge[maxm<<1];
int head[maxn] , dfn[maxn] , low[maxn] , vis[maxm<<1];
int stack[maxn] , isstack[maxn] ,value[maxn] ,dp[maxn];
int nedge , top , num , step ,sum;
int n , m ;int belong[maxn] , stu[maxn];
void addedge(int u , int v)
{
edge[nedge].v = v ;
edge[nedge].next = head[u] ;
head[u] = nedge++ ;
}
vector<int> vec[maxn] ;
void init()
{
memset(vis , 0 ,sizeof(vis)) ;
memset(dfn , 0 ,sizeof(dfn)) ;
memset(low , 0 , sizeof(low)) ;
memset(isstack , 0 , sizeof(isstack)) ;
memset(value , 0 , sizeof(value));
memset(head ,-1 , sizeof(head)) ;
memset(dp , 0 , sizeof(dp)) ;
for(int i = 0 ;i <= n;i++)
vec[i].clear() ;
top = num = step = nedge = sum = 0 ;
}
void tarjan(int u)
{
isstack[u] = 1 ;
stack[++top] = u ;
dfn[u] = low[u] = ++step;
for(int i = head[u];i != -1 ; i = edge[i].next)
{
if(vis[i])continue ;
vis[i] = vis[i^1] = 1 ;
int v = edge[i].v ;
if(!dfn[v])
{
tarjan(v) ;
low[u] = min(low[u] , low[v]) ;
}
else if(isstack[v])
low[u] = min(low[u] , dfn[v]) ;
}
if(dfn[u] == low[u])
{
num++ ;
int v ;
while(u!=v)
{
v = stack[top--] ;
belong[v] = num ;
isstack[v] = 0 ;
value[num] += stu[v] ;
}
}
}
void build_tree()
{
for(int i = 1;i <= n;i++)
for(int j = head[i] ; j != -1 ;j = edge[j].next)
{
int u = belong[i] ;
int v = belong[edge[j].v] ;
if(u == v)continue ;
vec[u].push_back(v);
}
}
void dfs(const int u , int &ans)
{
vis[u] = 1;
for(int i = 0;i < vec[u].size();i++)
{
int v = vec[u][i] ;
if(vis[v])continue ;
dfs(v , ans) ;
ans = min(ans , (int)(abs((double)(sum - 2*dp[v])))) ;
dp[u] += dp[v] ;
}
dp[u] += value[u];
}
int main()
{
//freopen("in.txt" , "r" , stdin) ;
while(~scanf("%d%d" , &n , &m))
{
int a , b ;
init() ;
for(int i = 1;i <= n;i++)
{
scanf("%d" , &stu[i]) ;
sum += stu[i] ;
}
for(int i = 1;i <= m;i++)
{
scanf("%d%d" , &a , &b) ;
addedge(a+1 , b+1) ;
addedge(b+1 , a+1) ;
}
int ans = inf ;
tarjan(1) ;
build_tree() ;
if(num <= 1)puts("impossible") ;
else
{
memset(vis , 0 , sizeof(vis)) ;
dfs(1 , ans) ;
printf("%d\n" , ans) ;
}
}
return 0 ;
}