zoj 月赛

/*Author :usedrose  */
/*Created Time :2015/7/26 22:29:35*/
/*File Name :2.cpp*/
#include <cstdio>
#include <iostream>
#include <algorithm>
#include <sstream>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <vector>
#include <string>
#include <ctime>
#include <cmath>
#include <deque>
#include <queue>
#include <stack>
#include <set>
#include <map>
#define INF 0x3f3f3f3f
#define eps 1e-8
#define pi acos(-1.0)
#define OK cout << "ok" << endl;
#define o(a) cout << #a << " = " << a << endl
#define o1(a,b) cout << #a << " = " << a << "  " << #b << " = " << b << endl
using namespace std;
typedef long long LL;

//最小费用最大流，求最大费用只需要取相反数，结果取相反数即可。
//点的总数为 N，点的编号 0~N-1
const int MAXN = 10000;
const int MAXM = 100000;

int n,m;

int A[MAXN],B[MAXN],X[MAXN],Y[MAXN];

struct Edge
{
int to,next,cap,flow,cost;
}edge[MAXM];
int head[MAXN],tol;
int pre[MAXN],dis[MAXN];
bool vis[MAXN];
int N;//节点总个数，节点编号从0~N-1

void init(int n)
{
N = n;
tol = 0;
memset(head,-1,sizeof(head));
}

void addedge(int u,int v,int cap,int cost)
{
edge[tol].to = v;
edge[tol].cap = cap;
edge[tol].cost = cost;
edge[tol].flow = 0;
edge[tol].next = head[u];
head[u] = tol++;
edge[tol].to = u;
edge[tol].cap = 0;
edge[tol].cost = -cost;
edge[tol].flow = 0;
edge[tol].next = head[v];
head[v] = tol++;
}

bool spfa(int s,int t)
{
queue<int>q;
for(int i = 0;i < N;i++)
{
dis[i] = INF;
vis[i] = false;
pre[i] = -1;
}
dis[s] = 0;
vis[s] = true;
q.push(s);
while(!q.empty())
{
int u = q.front();
q.pop();
vis[u] = false;
for(int i = head[u]; i != -1;i = edge[i].next)
{
int v = edge[i].to;
if(edge[i].cap > edge[i].flow && dis[v] > dis[u] + edge[i].cost )
{
dis[v] = dis[u] + edge[i].cost;
pre[v] = i;
if(!vis[v])
{
vis[v] = true;
q.push(v);
}
}
}
}
if(pre[t] == -1) return false;
else return true;
}

//返回的是最大流， cost存的是最小费用
int minCostMaxflow(int s,int t,int &cost)
{
int flow = 0;
cost = 0;
while(spfa(s,t))
{
int Min = INF;
for(int i = pre[t];i != -1;i = pre[edge[i^1].to])
{
if(Min > edge[i].cap - edge[i].flow)
Min = edge[i].cap - edge[i].flow;
}
for(int i = pre[t];i != -1;i = pre[edge[i^1].to])
{
edge[i].flow += Min;
edge[i^1].flow -= Min;
cost += edge[i].cost * Min;
}
flow += Min;
}
return flow;
}

int main()
{
//freopen("data.in","r",stdin);
//freopen("data.out","w",stdout);
cin.tie(0);
ios::sync_with_stdio(false);
while (cin >> n >> m) {
int all = 0;
init(n+2);
int s = 0, t = n+1;
for (int i = 1;i <= n; ++ i) {
cin >> A[i] >> B[i];
if (A[i] > B[i])
addedge(s, i, A[i]-B[i], 0);
else if (A[i] < B[i]) {
addedge(i, t, B[i]-A[i], 0);
all += (B[i] - A[i]);
}
}
int u, v;
for (int i = 0;i < m; ++ i) {
cin >> u >> v;
addedge(u, v, INF, 1);
addedge(v, u, INF, 1);
}
int cost, ans;
ans = minCostMaxflow(s, t, cost);
if (ans < all) cout << -1 << endl;
else cout << cost << endl;
}
return 0;
}