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

#define rng(i,a,b) for(int i=(int)a;i<(int)b;i++)
#define rep(i,b) rng(i,0,b)
#define repn(i,b) rng(i,1,b+1)
#define pb push_back
#define eb emplace_back
#define si(x) (int)(x.size())

#define tct template<class t>
#define tctu template<class t, class u>
tctu bool chmax(t&a, u b){if(a<b){a=b;return 1;}return 0;}
tctu bool chmin(t&a, u b){if(a>b){a=b;return 1;}return 0;}
tct using vc=vector<t>;
using vi=vc<int>;
using P=pair<int,int>;
#define a first
#define b second
#define mp make_pair

pair<ll,ll>get(int a,int b,int c,int d,int e){
	if(a == e) return mp(c, 1);
	if(b == e) return mp(d, 1);
	int up = d-c;
	int dw = b-a;
	pair<ll,ll>ret = mp(1LL*c*dw, dw);
	ret.a += up*(e-a);
	return ret;
}
pair<ll, ll>get_mn(pair<ll,ll>x, pair<ll,ll>y){
	//x.a/x.b < y.a/y.b?
	__int128 le = (__int128)x.a * y.b;
	__int128 ri = (__int128)y.a * x.b;
	if(le < ri) return x;
	return y;
}
struct seg{
	//(a,c)-(b,d)
	//a<b
	int a,b,c,d;
	seg(int A,int B,int C,int D){
		a=A,b=B,c=C,d=D;
	}
	bool operator<(const seg &s)const{
		if(a==s.a and b==s.b and c==s.c and d==s.d)return 0;
		int mn = min(b, s.b);
		int mx = max(a, s.a);
		if(mn < mx) return false;
		auto xa = get(a,b,c,d,mn);
		auto xb = get(a,b,c,d,mx);
		xa = get_mn(xa, xb);
		auto xc = get(s.a,s.b,s.c,s.d,mn);
		auto xd = get(s.a,s.b,s.c,s.d,mx);
		xc = get_mn(xc, xd);
		return get_mn(xa, xc) == xc;
	}
};
int lb, ub, n;
vi za;
vc<tuple<int,int,int,int>>vec;
P Q[1000005];
set<seg>S;
map<int,int>M;
int in[500005];
vi edge[500005];

struct st{
	vi val;
	int nn;
	void init(int sz){
		nn=1;
		while(sz+5>=nn) nn<<=1;
		val.assign(nn+nn, 0);
	}
	int get(int vall,int k,int l,int r){
		if(l == r) return val[k];
		if(vall <= (l+r)/2) return val[k] + get(vall, k*2+1, l, (l+r)/2);
		return val[k] + get(vall, k*2+2, (l+r)/2+1, r);
	}
	void upd(int le, int ri, int add, int k,int l,int r){
		if(le>ri or ri<l or r<le) return;
		if(le <= l and r <= ri){
			val[k]+=add;
			return;
		}
		upd(le,ri,add,k*2+1,l,(l+r)/2);
		upd(le,ri,add,k*2+2,(l+r)/2+1,r);
	}
	int get(int val){ return get(val,0,0,nn-1); }
	void upd(int le,int ri,int add){ upd(le,ri,add,0,0,nn-1); }
}s;

void solve(){
	cin>>lb>>ub>>n;
	za.pb(lb); za.pb(ub);
	rep(i,n){
		int ax,ay,bx,by;
		cin>>ax>>ay>>bx>>by;
		if(ax > bx){
			swap(ax, bx);
			swap(ay, by);
		}
		vec.eb(ax,bx,ay,by);
		za.pb(ax);
		za.pb(bx);
		M[ax] = i;
		M[bx] = i;
	}
	sort(za.begin(), za.end());
	za.erase(unique(za.begin(), za.end()), za.end());
	if(si(za) != 2*n+2) return;
	rep(i,n){
		Q[lower_bound(za.begin(), za.end(), get<0>(vec[i]))-za.begin()] = mp(1, i);
		Q[lower_bound(za.begin(), za.end(), get<1>(vec[i]))-za.begin()] = mp(2, i);
	}
	rep(i,si(za)){
		{
			auto [ty, id]=Q[i];
			if(!ty) continue;
			auto [a,b,c,d]=vec[id];
			if(ty == 2){
				S.erase(S.find(seg(a,b,c,d)));
			}
			else if(ty == 1){
				auto it = S.lower_bound(seg(a,b,c,d));
				if(it != S.end()){
					int v = (*it).a;
					edge[id].pb(M[v]);
					in[M[v]] ++;
				}
				if(it != S.begin()){
					it --;
					int v = (*it).a;
					edge[M[v]].pb(id);
					in[id] ++;
				}
				S.insert(seg(a,b,c,d));
			}
		}
	}
	queue<int>que;
	rep(i,n) if(!in[i]) que.push(i);
	vi ord;
	while(!que.empty()){
		int q = que.front(); que.pop();
		ord.pb(q);
		for(auto to:edge[q]){
			in[to]--;
			if(!in[to]) que.push(to);
		}
	}
	set<int>up,dw;
	set<int>dif;
	s.init(si(za));
	auto add=[&](int l,int r,int v){
		if(l){
			int le = s.get(l-1);
			int ri = s.get(l);
			if(le != ri){
				dif.erase(l-1);
			}
			if(le < ri) up.erase(l-1);
			if(le > ri) dw.erase(l-1);
			if(le != ri+v){
				dif.insert(l-1);
			}
			if(le < ri+v) up.insert(l-1);
			if(le > ri+v) dw.insert(l-1);
		}
		if(r+1 < si(za)){
			int le = s.get(r);
			int ri = s.get(r+1);
			if(le != ri){
				dif.erase(r);
			}
			if(le < ri) up.erase(r);
			if(le > ri) dw.erase(r);
			if(le+v != ri){
				dif.insert(r);
			}
			if(le+v < ri) up.insert(r);
			if(le+v > ri) dw.insert(r);
		}
		s.upd(l,r,v);
	};
	rng(i,0,si(za)){
		if(lb <= za[i] and za[i] <= ub);
		else {
			add(i,i,1000000);
		}
	}
	int loop=0,loop1=0;
	for(auto id:ord){
		int mn = lower_bound(za.begin(), za.end(), get<0>(vec[id])) - za.begin();
		int mx = lower_bound(za.begin(), za.end(), get<1>(vec[id])) - za.begin();
		int ay = get<2>(vec[id]);
		int by = get<3>(vec[id]);
		if(ay > by){
			int cur = mn;	
			while(1){
				auto it0 = up.lower_bound(cur);
				if(it0 == up.end() or (*it0) >= mx) goto end;
				cur = (*it0);
				int dp = s.get(cur);
				while(1){
					auto it = dif.lower_bound(cur);
					if(it == dif.end() or (*it) >= mx) goto end;
					int nxtpos = *it;
					int nxtdp = s.get(nxtpos+1);
					if(dp >= nxtdp){
						cur = nxtpos+1;
						break;
					}
					else{
						auto it2 = it; it2++;
						int nxt2pos;
						if(it2 == dif.end() or (*it2) >= mx) nxt2pos = mx;
						else nxt2pos = *it2;
						
						add(nxtpos+1, nxt2pos, dp-nxtdp);
						loop++;
					}
				}
			}
			end:;
			add(mn+1, mx-1, 1);
		}
		else{
			int cur = mx;	
			while(1){
				auto it0 = dw.lower_bound(cur);
				if(it0 == dw.begin()) goto end2;
				it0--;
				if((*it0) < mn) goto end2;
				cur = (*it0)+1;
				int dp = s.get(cur);
				while(1){
					auto it = dif.lower_bound(cur);
					if(it == dif.begin()) goto end2;
					it --;
					if((*it) < mn) goto end2;
					int nxtpos = (*it);
					int nxtdp = s.get(nxtpos);
					if(dp >= nxtdp){
						cur = nxtpos;
						break;
					}
					else{
						auto it2 = it;
						int nxt2pos;
						if(it2 == dif.begin()) nxt2pos = mn;
						else{
							it2--;
							if((*it2)<mn) nxt2pos = mn;
							else nxt2pos = (*it2)+1;
						}
						
						add(nxt2pos, nxtpos, dp-nxtdp);
						loop1++;
					}
				}
			}
			end2:;
			add(mn+1, mx-1, 1);
		}
	}
	lb = lower_bound(za.begin(), za.end(), lb)-za.begin();
	ub = lower_bound(za.begin(), za.end(), ub)-za.begin();
	int ans = 1000000000;
	rng(i,lb,ub+1) chmin(ans,s.get(i));
	cout<<ans<<'\n';
}
signed main(){
	cin.tie(0);
	ios::sync_with_stdio(0);
	cout<<fixed<<setprecision(20);
	solve();
}