#include <iostream>
#include <cstdio>
using namespace std;

int N,M,A,B,C,D,x1,x2,y1,y2;
int K[32][32];
const int inf = 100;

int main(){
  for (int m=0; m < 32; m++){
  for (int n=0; n < 32; n++){
    K[m][n] = inf;
	}
  }
  scanf("%d%d", &N,&M);
  for (int i=0; i<=M-1; ++i) {
    scanf("%d,%d,%d,%d", &A,&B, &C, &D);
	K[A][B] = C;
	K[B][A] = D;
	}
	scanf("%d,%d,%d,%d", &x1,&x2, &y1, &y2);
	
  for (int k=1; k <= N; k++){
    for (int i=1; i <= N; i++){
	  for (int j=1; j <= N; j++){
	    if (K[i][j] > K[i][k] + K[k][j]){
		  K[i][j] = K[i][k] + K[k][j];
		  }
		}
	}
  }
  
int money = y1 -y2 -K[x1][x2] - K[x2][x1];
cerr << money << endl;
}