#include <stdio.h>
#include <string.h>
#include <algorithm>
#define min(a, b) ((a) < (b) ? (a) : (b))
#define REP(i, n) for(int i = 1; i <= n; ++i)
#define MS0(X) memset(X,  0, sizeof X)
#define MS1(X) memset(X, -1, sizeof X)
using namespace std;
const int maxE = 3000000;
const int maxN = 105;
const int oo = 0x3f3f3f3f;
struct Edge{
    int v, c, w, n;
};
Edge edge[maxE];
int adj[maxN], l;
int d[maxN], cur[maxN], a[maxN];
int inq[maxN], Q[maxE], head, tail;
int cost, flow, s, t;
int n, m, S, T;
int deg[maxN];
void addedge(int u, int v, int c, int w){
    edge[l].v = v; edge[l].c = c; edge[l].w =  w; edge[l].n = adj[u]; adj[u] = l++;
    edge[l].v = u; edge[l].c = 0; edge[l].w = -w; edge[l].n = adj[v]; adj[v] = l++;
}
int SPFA(){
    memset(d, oo, sizeof d);
    memset(inq, 0, sizeof inq);
    head = tail = 0;
    d[s] = 0;
    a[s] = oo;
    cur[s] = -1;
    Q[tail++] = s;
    while(head != tail){
        int u =  Q[head++];
        inq[u] = 0;
        for(int i = adj[u]; ~i; i = edge[i].n){
            int v = edge[i].v;
            if(edge[i].c && d[v] > d[u] + edge[i].w){
                d[v] = d[u] + edge[i].w;
                cur[v] = i;
                a[v] = min(edge[i].c, a[u]);
                if(!inq[v]){
                    inq[v] = 1;
                    Q[tail++] = v;
                }
            }
        }
    }
    if(d[t] == oo) return 0;
    flow += a[t];
    cost += a[t] * d[t];
    for(int i = cur[t]; ~i; i = cur[edge[i ^ 1].v]){
        edge[i].c -= a[t];
        edge[i ^ 1].c += a[t];
    }
    return 1;
}
int MCMF(){
    flow = cost = 0;
    while(SPFA());
    return flow;
}
void work(){
    int u, v, a, b, sum = 0;
    scanf("%d%d%d%d", &n, &m, &S, &T);
    MS1(adj);
    MS0(deg);
    l = 0;
    while(m--){
        scanf("%d%d%d%d", &u, &v, &a, &b);
        if(a > b){
            addedge(v, u, 1, a - b);
            sum += b;
        }
        else{
            addedge(u, v, 1, b - a);
            sum += a;
            ++deg[u];
            --deg[v];
        }
    }
    ++deg[T];
    --deg[S];
    s = 0; t = n + 1;
    int nflow = 0;
    REP(i, n){
        if(deg[i] > 0){
            addedge(s, i, deg[i], 0);
            nflow += deg[i];
        }
        if(deg[i] < 0){
            addedge(i, t, -deg[i], 0);
        }
    }
    MCMF();
    if(nflow == flow){
        printf("%d\n", cost + sum);
    }
    else printf("impossible\n");
}
int main(){
    int T, cas;
    for(scanf("%d", &T), cas = 1; cas <= T; cas++){
        printf("Case %d: ", cas);
        work();
    }
    return 0;
}