#include <iostream>

#include <cstdio>

#include <sstream>

#include <cstring>

#include <map>

#include <cctype>

#include <set>

#include <vector>

#include <stack>

#include <queue>

#include <algorithm>

#include <cmath>

#include <bitset>

#define rap(i, a, n) for(int i=a; i<=n; i++)

#define rep(i, a, n) for(int i=a; i<n; i++)

#define lap(i, a, n) for(int i=n; i>=a; i--)

#define lep(i, a, n) for(int i=n; i>a; i--)

#define rd(a) scanf("%d", &a)

#define rlld(a) scanf("%lld", &a)

#define rc(a) scanf("%c", &a)

#define rs(a) scanf("%s", a)

#define pd(a) printf("%d\n", a);

#define plld(a) printf("%lld\n", a);

#define pc(a) printf("%c\n", a);

#define ps(a) printf("%s\n", a);

#define MOD 2018

#define LL long long

#define ULL unsigned long long

#define Pair pair<int, int>

#define mem(a, b) memset(a, b, sizeof(a))

#define _  ios_base::sync_with_stdio(0),cin.tie(0)

//freopen("1.txt", "r", stdin);

using namespace std;

const int maxn = , INF = 0x7fffffff, LL_INF = 0x7fffffffffffffff;

int k, n, m;

int dis[maxn][], vis[maxn][], head[maxn];

int cnt;

struct edge

{

    int u, v, d, t;

    edge(int u, int v, int d, int t) : u(u), v(v), d(d), t(t) {}

};

vector<edge> Edge;

vector<int> G[maxn << ];

struct node

{

    int u, d, t;

    node(int u, int d, int t) : u(u), d(d), t(t) {}

    bool operator < (const node &a) const {

        return d > a.d;

    }

};

void add(int u, int v, int d, int t)

{

    Edge.push_back(edge(u, v, d, t));

    G[u].push_back(Edge.size() - );

}

void dijkstra()

{

    priority_queue<node> Q;

    for(int i = ; i < maxn; i++) for(int j = ; j < ; j++) dis[i][j] = INF;

    mem(vis, );

    Q.push(node(, , ));

    dis[][] = ;

   // vis[0][1] = 1;

    while(!Q.empty())

    {

        node x = Q.top(); Q.pop();

        int u = x.u;

        int t = x.t;

        if(vis[t][u]) continue;

        vis[t][u] = ;

        for(int i = ; i < G[u].size(); i++)

        {

            edge e = Edge[G[u][i]];

            if(dis[t + e.t][e.v] > dis[t][u] + e.d && t + e.t <= k)

            {

                dis[t + e.t][e.v] = dis[t][u] + e.d;

                Q.push(node(e.v, dis[t + e.t][e.v], t + e.t));

            }

        }

    }

}

int main()

{

    int u, v, d, t;

    rd(k), rd(n), rd(m);

    for(int i = ; i <= m; i++)

    {

        rd(u), rd(v), rd(d), rd(t);

        add(u, v, d, t);

    }

    dijkstra();

    int maxx = INF;

    for(int i = ; i <= k; i++)

        maxx = min(maxx, dis[i][n]);

    if(maxx == INF)

        return puts("-1"), ;

    cout << maxx << endl;

    return ;

}