#include<bits/stdc++.h>
using namespace std;

#define all(a) a.begin(),a.end()
#define pb push_back
#define sz(a) ((int)a.size())

using ll=long long;
using u32=unsigned int;
using u64=unsigned long long;
using i128=__int128;
using u128=unsigned __int128;
using f128=__float128;

using pii=pair<int,int>;
using pll=pair<ll,ll>;

template<typename T> using vc=vector<T>;
template<typename T> using vvc=vc<vc<T>>;
template<typename T> using vvvc=vc<vvc<T>>;

using vi=vc<int>;
using vll=vc<ll>;
using vvi=vc<vi>;
using vvll=vc<vll>;

#define vv(type,name,n,...) \
    vector<vector<type>> name(n,vector<type>(__VA_ARGS__))
#define vvv(type,name,n,m,...) \
    vector<vector<vector<type>>> name(n,vector<vector<type>>(m,vector<type>(__VA_ARGS__)))

template<typename T> using min_heap=priority_queue<T,vector<T>,greater<T>>;
template<typename T> using max_heap=priority_queue<T>;

// https://trap.jp/post/1224/
#define rep1(n) for(ll i=0; i<(ll)(n); ++i)
#define rep2(i,n) for(ll i=0; i<(ll)(n); ++i)
#define rep3(i,a,b) for(ll i=(ll)(a); i<(ll)(b); ++i)
#define rep4(i,a,b,c) for(ll i=(ll)(a); i<(ll)(b); i+=(c))
#define cut4(a,b,c,d,e,...) e
#define rep(...) cut4(__VA_ARGS__,rep4,rep3,rep2,rep1)(__VA_ARGS__)
#define per1(n) for(ll i=((ll)n)-1; i>=0; --i)
#define per2(i,n) for(ll i=((ll)n)-1; i>=0; --i)
#define per3(i,a,b) for(ll i=((ll)a)-1; i>=(ll)(b); --i)
#define per4(i,a,b,c) for(ll i=((ll)a)-1; i>=(ll)(b); i-=(c))
#define per(...) cut4(__VA_ARGS__,per4,per3,per2,per1)(__VA_ARGS__)
#define rep_subset(i,s) for(ll i=(s); i>=0; i=(i==0?-1:(i-1)&(s)))

template<typename T, typename S> constexpr T ifloor(const T a, const S b){return a/b-(a%b&&(a^b)<0);}
template<typename T, typename S> constexpr T iceil(const T a, const S b){return ifloor(a+b-1,b);}

template<typename T>
void sort_unique(vector<T> &vec){
    sort(vec.begin(),vec.end());
    vec.resize(unique(vec.begin(),vec.end())-vec.begin());
}

template<typename T, typename S> constexpr bool chmin(T &a, const S b){if(a>b) return a=b,true; return false;}
template<typename T, typename S> constexpr bool chmax(T &a, const S b){if(a<b) return a=b,true; return false;}

template<typename T, typename S> istream& operator >> (istream& i, pair<T,S> &p){return i >> p.first >> p.second;}
template<typename T, typename S> ostream& operator << (ostream& o, const pair<T,S> &p){return o << p.first << ' ' << p.second;}

#ifdef i_am_noob
#define bug(...) cerr << "#" << __LINE__ << ' ' << #__VA_ARGS__ << "- ", _do(__VA_ARGS__)
template<typename T> void _do(vector<T> x){for(auto i: x) cerr << i << ' ';cerr << "\n";}
template<typename T> void _do(set<T> x){for(auto i: x) cerr << i << ' ';cerr << "\n";}
template<typename T> void _do(unordered_set<T> x){for(auto i: x) cerr << i << ' ';cerr << "\n";}
template<typename T> void _do(T && x) {cerr << x << endl;}
template<typename T, typename ...S> void _do(T && x, S&&...y) {cerr << x << ", "; _do(y...);}
#else
#define bug(...) 777771449
#endif

template<typename T> void print(vector<T> x){for(auto i: x) cout << i << ' ';cout << "\n";}
template<typename T> void print(set<T> x){for(auto i: x) cout << i << ' ';cout << "\n";}
template<typename T> void print(unordered_set<T> x){for(auto i: x) cout << i << ' ';cout << "\n";}
template<typename T> void print(T && x) {cout << x << "\n";}
template<typename T, typename... S> void print(T && x, S&&... y) {cout << x << ' ';print(y...);}

template<typename T> istream& operator >> (istream& i, vector<T> &vec){for(auto &x: vec) i >> x; return i;}

vvi read_graph(int n, int m, int base=1){
    vvi adj(n);
    for(int i=0,u,v; i<m; ++i){
        cin >> u >> v,u-=base,v-=base;
        adj[u].pb(v),adj[v].pb(u);
    }
    return adj;
}

vvi read_tree(int n, int base=1){return read_graph(n,n-1,base);}

template<typename T, typename S> pair<T,S> operator + (const pair<T,S> &a, const pair<T,S> &b){return {a.first+b.first,a.second+b.second};}

template<typename T> constexpr T inf=0;
template<> constexpr int inf<int> = 0x3f3f3f3f;
template<> constexpr ll inf<ll> = 0x3f3f3f3f3f3f3f3f;

template<typename T> vector<T> operator += (vector<T> &a, int val){for(auto &i: a) i+=val; return a;}

template<typename T> T isqrt(const T &x){T y=sqrt(x+2); while(y*y>x) y--; return y;}

#define ykh mt19937 rng(chrono::steady_clock::now().time_since_epoch().count())

#include<atcoder/all>
using namespace atcoder;

using mint=modint998244353;
//using mint=modint1000000007;

template<typename T>
vector<T> dijkstra(int s, vector<vector<pair<int,T>>> adj){
    int n=sz(adj);
    vector<T> dis(n,inf<T>);
    vector<int> vis(n);
    priority_queue<pair<T,int>,vector<pair<T,int>>,greater<pair<T,int>>> pq;
    dis[s]=0,pq.push({0,s});
    while(!pq.empty()){
        auto [d,u]=pq.top(); pq.pop();
        if(vis[u]) continue;
        vis[u]=1;
        for(auto &[v,w]: adj[u]) if(d+w<dis[v]){
            dis[v]=d+w;
            pq.push({dis[v],v});
        }
    }
    return dis;
}

void ahcorz(){
    int n,m,k; cin >> n >> m >> k;
    vi a(k),b(k),c(k),d(k),tmp1,tmp2;
    tmp1.pb(0),tmp1.pb(n-1),tmp2.pb(0),tmp2.pb(m-1);
    rep(k) cin >> a[i] >> b[i] >> c[i] >> d[i],a[i]--,b[i]--,c[i]--,d[i]--,tmp1.pb(a[i]),tmp2.pb(b[i]),tmp1.pb(c[i]),tmp2.pb(d[i]);
    sort_unique(tmp1),sort_unique(tmp2);
    vvc<pair<int,ll>> adj(sz(tmp1)*sz(tmp2));
    /*
    rep(sz(tmp1)) rep(j,sz(tmp2)-1){
        adj[i*sz(tmp2)+j].pb({i*sz(tmp2)+j+1,tmp2[j+1]-tmp2[j]});
        adj[i*sz(tmp2)+j+1].pb({i*sz(tmp2)+j,tmp2[j+1]-tmp2[j]});
    }
    rep(sz(tmp1)-1) rep(j,sz(tmp2)){
        adj[i*sz(tmp2)+j].pb({(i+1)*sz(tmp2)+j,tmp1[i+1]-tmp1[i]});
        adj[(i+1)*sz(tmp2)+j].pb({i*sz(tmp2)+j,tmp1[i+1]-tmp1[i]});
    }
    */
    rep(k){
        a[i]=lower_bound(all(tmp1),a[i])-tmp1.begin();
        b[i]=lower_bound(all(tmp2),b[i])-tmp2.begin();
        c[i]=lower_bound(all(tmp1),c[i])-tmp1.begin();
        d[i]=lower_bound(all(tmp2),d[i])-tmp2.begin();
        adj[a[i]*sz(tmp2)+b[i]].pb({c[i],d[i]});
    }
    vv(ll,dis,sz(tmp1),sz(tmp2),inf<ll>);
    dis[0][0]=0;
    max_heap<pair<ll,pii>> pq;
    pq.push({0,pii(0,0)});
    int dx[4]={0,1,0,-1},dy[4]={1,0,-1,0};
    while(!pq.empty()){
        auto [d,p]=pq.top(); pq.pop();
        auto [i,j]=p;
        if(d!=dis[i][j]) continue;
        for(auto &[ni,nj]: adj[i*sz(tmp2)+j]) if(d+1<dis[ni][nj]){
            dis[ni][nj]=d+1;
            pq.push({dis[ni][nj],pii(ni,nj)});
        }
        rep(de,4){
            int ni=i+dx[de],nj=j+dy[de];
            if(ni>=0&&ni<sz(tmp1)&&nj>=0&&nj<sz(tmp2)){
                ll nw=d;
                if(dx[de]==1) nw+=tmp1[i+1]-tmp1[i];
                if(dx[de]==-1) nw+=tmp1[i]-tmp1[i-1];
                if(dy[de]==1) nw+=tmp2[j+1]-tmp2[j];
                if(dy[de]==-1) nw+=tmp2[j]-tmp2[j-1];
                if(nw<dis[ni][nj]){
                    dis[ni][nj]=nw;
                    pq.push({dis[ni][nj],pii(ni,nj)});
                }
            }
        }
    }
    //rep(sz(adj)) for(auto &[j,val]: adj[i]) bug(i,j,val);
    print(dis[sz(tmp1)-1][sz(tmp2)-1]);
}

signed main(){
    ios_base::sync_with_stdio(0),cin.tie(0);
    cout << fixed << setprecision(20);
    int t=1;
    //cin >> t;
    while(t--) ahcorz();
}