#ifdef NACHIA
#define _GLIBCXX_DEBUG
#else
#define NDEBUG
#endif
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <queue>
#include <array>
#include <cmath>
#include <atcoder/modint>
using i64 = long long;
using u64 = unsigned long long;
#define rep(i,n) for(i64 i=0; i<(i64)(n); i++)
#define repr(i,n) for(i64 i=(i64)(n)-1; i>=0; i--)
const i64 INF = 1001001001001001001;
const char* yn(bool x){ return x ? "Yes" : "No"; }
template<typename A> void chmin(A& l, const A& r){ if(r < l) l = r; }
template<typename A> void chmax(A& l, const A& r){ if(l < r) l = r; }
template<typename A> using nega_queue = std::priority_queue<A,std::vector<A>,std::greater<A>>;
using Modint = atcoder::static_modint<998244353>;
//#include "nachia/vec.hpp"
using namespace std;

void testcase(){
    i64 H, W, N; cin >> H >> W >> N;
    vector<i64> A(N+1), B(N+1), C(N), D(N);
    rep(i,N) cin >> A[i] >> B[i] >> C[i] >> D[i];
    A[N] = H; B[N] = W;
    vector<i64> dist(N+1);
    rep(i,N+1) dist[i] = A[i] + B[i] - 2;
    vector<int> vis(N+1);
    rep(i,N+1){
        int nx = -1;
        rep(j,N+1) if(vis[j] == 0) if(nx == -1 || dist[j] < dist[nx]) nx = j;
        vis[nx] = 1;
        if(nx == N){ cout << dist[N] << endl; break; }
        rep(p,N+1){
            i64 d = abs(A[p] - C[nx]) + abs(B[p] - D[nx]) + 1;
            chmin(dist[p], dist[nx] + d);
        }
    }
}

int main(){
    ios::sync_with_stdio(false); cin.tie(nullptr);
    #ifdef NACHIA
    int T; cin >> T; for(int t=0; t<T; T!=++t?(cout<<'\n'),0:0)
    #endif
    testcase();
    return 0;
}