#include<bits/stdc++.h>
#define int long long
#define mk make_pair
#define PII pair<int,int>
#define FOR(i,j,k) for(int i=(j);i<=(k);++i)
#define ROF(i,j,k) for(int i=(j);i>=(k);--i)
#define FOI(a,b) for(auto a : b)
#define wh while
#define inf 0x3f3f3f3f3f3f3f3f
#define IOS ios::sync_with_stdio(false);
#define snd second
#define fst first
#define pb push_back
#define CI const int
#define NP namespace
using NP std;
struct eg
{
	int v,mo,op;
};
int n,m,p;
vector<eg> g[20005];
int mc[20005];
int d[20005][22];
struct nd
{
	int u,l,di;
	bool operator<(const nd& o)const
	{
		return di>o.di;
	}
};
signed main(void)
{
	freopen("levelup.in","r",stdin);
	freopen("levelup.out","w",stdout);
	IOS
	cin>>n>>m>>p;
	FOR(i,1,m)
	{
		int u,v,mo,op;
		cin>>u>>v>>mo>>op;
		g[u].pb({v,mo,op});
	}
	FOR(i,1,20000)
	{
		mc[i]=inf;
	}
	FOR(i,1,p)
	{
		int po,c;
		cin>>po>>c;
		mc[po]=min(mc[po],c);
	}
	int st,ed;
	cin>>st>>ed;
	FOR(i,1,n)
	{
		FOR(j,0,21)
		{
			d[i][j]=inf;
		}
	}
	priority_queue<nd> pq;
	d[st][0]=0;
	pq.push({st,0,0});
	wh(!pq.empty())
	{
		nd cu=pq.top();
		pq.pop();
		int u=cu.u,l=cu.l,di=cu.di;
		if(di>d[u][l])
		{
			continue;
		}
		if(l<21&&mc[u]!=inf)
		{
			if(d[u][l+1]>di+mc[u])
			{
				d[u][l+1]=di+mc[u];
				pq.push({u,l+1,d[u][l+1]});
			}
		}
		FOI(e,g[u])
		{
			int lv=(1LL<<l);
			int w=(e.mo+lv-1)/lv;
			int nl=(e.op==1)?0:l;
			if(d[e.v][nl]>di+w)
			{
				d[e.v][nl]=di+w;
				pq.push({e.v,nl,d[e.v][nl]});
			}
		}
	}
	int ans=inf;
	FOR(j,0,21)
	{
		ans=min(ans,d[ed][j]);
	}
	if(ans==inf)
	{
		cout<<"Impossible!\n";
	}
	else
	{
		cout<<ans<<"\n";
	}
	return 0;
}