#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define v vector
#define lp(i, s, e) for (ll i = s; i < e; ++i)
#define tpl tuple<ll, ll, ll, ll, ll, ll>
struct Seg {
Seg *left = nullptr, *right = nullptr;
int l, r, mid;
int id = -1, lazy = -1;
Seg(int l, int r) : l(l), r(r), mid((l + r) / 2) {}
void ensure() {
if (l == r)
return;
if (left == nullptr) {
left = new Seg(l, mid);
right = new Seg(mid + 1, r);
}
}
void push() {
if (lazy == -1)
return;
id = lazy;
ensure();
if (l != r) {
left->lazy = lazy;
right->lazy = lazy;
}
lazy = -1;
}
int q(int pos) {
push();
if (l == r)
return id;
ensure();
if (pos <= mid)
return left->q(pos);
return right->q(pos);
}
void update(int a, int b, int V) {
push();
if (l > b || r < a)
return;
if (l >= a && r <= b) {
lazy = V;
push();
return;
}
ensure();
left->update(a, b, V);
right->update(a, b, V);
}
};
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
ll dest_x, dest_y;
cin >> dest_x >> dest_y;
ll n;
cin >> n;
vector<tpl> vec;
v<ll> y_val;
y_val.push_back(dest_y);
y_val.push_back(0);
v<ll> B_bottom(n + 2), B_top(n + 2);
lp(i, 0, n) {
ll a, b, c, d;
cin >> a >> b >> c >> d;
if (a >= dest_x)
continue;
c = min(c, dest_x);
B_bottom[i + 1] = b;
B_top[i + 1] = d;
y_val.push_back(b);
y_val.push_back(d);
y_val.push_back(b - 1);
y_val.push_back(d + 1);
vec.push_back({a, b, c, d, 0, i + 1});
vec.push_back({c, d, a, b, 1, i + 1});
}
sort(y_val.begin(), y_val.end());
y_val.erase(unique(y_val.begin(), y_val.end()), y_val.end());
auto get_y = [&](ll y) {
return lower_bound(y_val.begin(), y_val.end(), y) - y_val.begin();
};
vec.push_back({0, 0, 0, 0, 1, 0});
sort(vec.begin(), vec.end());
Seg seg(0, y_val.size() - 1);
seg.update(0, y_val.size() - 1, n + 1);
v<v<ll>> dp(n + 2, v<ll>(2, 0));
auto get_dist = [&](ll y, int hit) {
if (hit == n + 1)
return abs(y - dest_y);
ll cost_bottom = abs(y - (B_bottom[hit] - 1)) + dp[hit][0];
ll cost_top = abs(y - (B_top[hit] + 1)) + dp[hit][1];
return min(cost_bottom, cost_top);
};
ll ans = 1e18;
for (auto it = vec.rbegin(); it != vec.rend(); ++it) {
auto [cx, cy, ox, oy, type, idx] = *it;
if (type == 1) {
if (idx == 0) {
int hit = seg.q(get_y(0));
ans = dest_x + get_dist(0, hit);
} else {
ll y_bottom = oy;
ll y_top = cy;
int hit1 = seg.q(get_y(y_bottom - 1));
dp[idx][0] = get_dist(y_bottom - 1, hit1);
int hit2 = seg.q(get_y(y_top + 1));
dp[idx][1] = get_dist(y_top + 1, hit2);
}
} else {
ll y_bottom = cy;
ll y_top = oy;
seg.update(get_y(y_bottom), get_y(y_top), idx);
}
}
cout << ans << "\n";
}
