#include<bits/stdc++.h>

#define fastio ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define ll long long
#define pii pair<int,int>
#define pill pair<int,ll>
#define pll pair<ll,ll>
#define pb push_back
#define fi first
#define se second
#define ff fi.fi
#define fs fi.se
#define sf se.fi
#define ss se.se
#define MASK(x) (((1)<<(x))-1)
#define getbit(x,k) (((x)>>(k))&1)

using namespace std;

const int maxn=1e5+5,mod=1e9+22071997;
const ll inf=1e18;

int n,m,k;
vector<pii>eg[maxn];
ll d[2][maxn];
void dijkstra(int s, ll f[])
{
    fill(f+1,f+1+n,inf);f[s]=0;
    priority_queue<pll,vector<pll>,greater<pll>>pQ;
    pQ.push({f[s],s});
    while(pQ.size())
    {
        pll u=pQ.top();pQ.pop();
        if(u.fi!=f[u.se]) continue;
        for(pii v:eg[u.se]) if(u.fi+v.se<f[v.fi])
        {
            f[v.fi]=u.fi+v.se;
            pQ.push({f[v.fi],v.fi});
        }
    }
}
int main()
{
    cin>>n>>m>>k;
    for(int i=1;i<=m;i++)
    {
        int u,v,c;cin>>u>>v>>c;
        eg[u].pb({v,c});//eg[v].pb({u,c});
    }
    dijkstra(1,d[0]);dijkstra(n,d[1]);
    while(k--)
    {
        ll a,b,ans=inf;cin>>a>>b;
        for(int i=1;i<=n;i++)
            if(d[0][i]!=inf && d[1][i]!=inf)
                ans=min(ans,d[0][i]*a+d[1][i]*b);
        cout<<ans<<'\n';
    }
}