#if 0

#endif


#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=1001001001;

int main() {
	long long pay,ans;
	for(int i=0;i<32;i++)
		for(int j=0;j<32;j++)
			K[i][j]=inf;

	scanf("%d%d", &N, &M);
	for (int i=0; i<M; ++i) {
		scanf("%d,%d,%d,%d", &A, &B, &C, &D);
		//cerr << "read " << A <<" "<< B <<" " << C <<" " << D<< endl;
		//?????????
		K[A][B]=C; // A ??? B ????????????C
		K[B][A]=D;// B ??? A ????????????D    
	}
	/*
	for(int i=1;i<N+1;i++){//?????§?????????
		for(int j=1;j<N+1;j++){
			if(K[i][j]==inf){
	cout<<"i"<<" ";
			}else{
	cout<<K[i][j]<<" ";
			}
		}
		cout<<endl;
	}
	*/
	for(int k=1;k<N+1;k++){
		for(int i=1;i<N+1;i++){
			for(int j=1;j<N+1;j++){
	if(K[i][j]>K[i][k]+K[k][j]){
		K[i][j]=K[i][k]+K[k][j];
	}
			}
		}/*
		for(int l=1;l<N+1;l++){//?????§??????2???
		for(int m=1;m<N+1;m++){
			if(K[l][m]==inf){
	cout<<"i"<<" ";
			}else{
	cout<<K[l][m]<<" ";
			}
		}
		cout<<endl;
		} 
		cout<<endl;*/
	}
	scanf("%d,%d,%d,%d", &A, &B, &C, &D);
	pay=K[A][B]+K[B][A];
	ans=C-D-pay;
	cout<<ans<<endl; 
}