#include <iostream>
#include<vector>
#include<queue>
using namespace std;
struct node
{
    int idx;
    int distance;
    int money;
    node(){}
    node(int _idx, int _distance, int _money)
    {
        idx=_idx;
        distance=_distance;
        money=_money;
    }
    bool operator < (const node &tmp) const{
        return distance > tmp.distance;
    }
};
int main()
{
    int s;
    int n,m;
    cin>>s>>n>>m;
    vector<node>v[n+1];
    for(int i=0; i<m;i++)
    {
        int a,b,c,d;
        cin>>a>>b>>c>>d;
        v[a].push_back(node(b,c,d));
        v[b].push_back(node(a,c,d));

    }
    int dis[n+1][s+1];
    for(int i=0;i<n+1;i++)
    {
        for(int j=0;j<s+1;j++)
        {
            dis[i][j]=2e9;
        }
    }
    priority_queue<node>pq;
    pq.push(node(1,0,0));
    while(!pq.empty())
    {
        node c=pq.top();
        pq.pop();

        for(int i=0;i< v[c.idx].size(); i++)
        {
            int sosed = v[c.idx][i].idx;
            int d = v[c.idx][i].distance;
                        int pari= v[c.idx][i].money;
                        if(pari+c.money<=s)
                        {
                            if(d+c.distance<dis[sosed][pari+c.money])
                            {
                                pq.push(node(sosed, d+c.distance,pari+c.money));
                                dis[sosed][pari+c.money]=d+c.distance;
                            }
                        }
                    }
                }
                int rez=2e9;
                for(int i=0;i<=s;i++)
                {
                  rez=min(rez,dis[n][i]);

                }
                if(rez==2e9)
                    cout<<-1;
                else
                    cout<<rez;
                return 0;
            }