#include <bits/stdc++.h> 

using i64 = long long; 
using u64 = unsigned long long; 
using u32 = unsigned; 

using u128 = unsigned __int128; 
using i128 = __int128; 

constexpr i64 inf = 1e18;

void solve() {
	i64 H, W; std::cin >> H >> W;
	int N; std::cin >> N;
	std::vector<i64> a(N), b(N), c(N), d(N);
	for(int i = 0; i < N; i ++) std::cin >> a[i] >> b[i] >> c[i] >> d[i];

	std::vector G(N + 2, std::vector<i64> (N + 2, -1));
	for(int i = 0; i < N; i ++) {
		G[0][i + 1] = a[i] + b[i] - 1;
	}
	G[0][N + 1] = H + W - 2;
	for(int i = 0; i < N; i ++) {
		for(int j = 0; j < N; j ++) {
			if(i == j) continue;
			G[i + 1][j + 1] = std::abs(a[j] - c[i]) + std::abs(b[j] - d[i]) + 1;
		}
	}
	for(int i = 0; i < N; i ++) {
		G[i + 1][N + 1] = H - c[i] + W - d[i];
	}
	
	std::priority_queue<std::pair<i64,int>, std::vector<std::pair<i64,int>>, std::greater<std::pair<i64,int>>> pq;
	pq.push({0, 0});
	std::vector<i64> ans(N + 2, inf);
	ans[0] = 0;
	while(!pq.empty()) {
		auto [x, y] = pq.top();
		pq.pop();
		for(int i = 0; i < N + 2; i ++) {
			if(G[y][i] == -1) continue;
			if(ans[i] <= x + G[y][i]) continue;
			else {
				ans[i] = x + G[y][i];
				pq.push({x + G[y][i], i});
			}
		}
	}

	std::cout << ans[N + 1];
} 

int main() { 
	std::ios::sync_with_stdio(false); 
	std::cin.tie(nullptr); 

	int T = 1; 
	//std::cin >> T; 

	while (T--) { 
		solve(); 
	} 
	return 0; 
}