#include <bits/stdc++.h>
using namespace std;
#define int long long
int n,m,k,v[200009];
vector<pair<int,pair<int,int> > > g[200009];
pair<int,int> d[200009];
void dijkstra(int v0)//(?
{
	for(int i=1;i<=n;i++) d[i].first=0x3f3f3f3f;
	priority_queue <pair<int,pair<int,int> >,vector<pair<int,pair<int,int> > >,greater<pair<int,pair<int,int> > > >q;
	d[0].first=0;
	q.push({v0,{0,0}});
	while(!q.empty())
	{
		auto x=q.top();
//		cout<<x.first<<" "<<x.second.first<<" "<<x.second.second<<'\n';
		q.pop();
		for(auto i:g[x.first])
		{
//			cout<<i.first<<" "<<i.second.first<<" "<<i.second.second<<'\n';
			if(d[i.first].first>x.second.first+i.second.first&&x.second.second+i.second.second<k)
			{
				d[i.first].first=x.second.first+i.second.first;
				d[i.first].second=x.second.second+i.second.second;
				q.push({i.first,{d[i.first].first,d[i.first].second}});
				v[i.first]=1;
			}
		}
	}
}
signed main()
{
//	freopen("hull.in","r",stdin);
//	freopen("hull.out","w",stdout);
	int x,y,ti,h;
	cin>>k>>n>>m;
	for(int i=1;i<=m;i++)
	{
		cin>>x>>y>>ti>>h;
		g[x].push_back({y,{ti,h}});
		g[y].push_back({x,{ti,h}});
	}
	int s,t;
	cin>>s>>t;
	dijkstra(s);
	if(v[t]||d[t].first!=0x3f3f3f3f) cout<<d[t].first<<'\n';
	else cout<<-1<<'\n';
	return 0;
}