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

int n, m;

int main(void){
	cin>>n;
	cin>>m;
	
	int a, b ,c , d, e ,f;
	
	
	if(n != 1){
		cout<<-1<<endl;
	}
	else{
		cin>>a>>b>>c>>d>>e>>f;
		if(f == 1){
			cout<<d-e+1;
		}
		else{
			cout<<a*b+ c*d - f;
		}
	}
	
	//cout<<endl;system("pause");
	return 0;
}