Example

Input

5 5 4
6
3 2
4 2
5 2
1 4
3 4
5 4


Output

6
#include<deque>
#include<queue>
#include<vector>
#include<algorithm>
#include<iostream>
#include<set>
#include<cmath>
#include<tuple>
#include<string>
#include<chrono>
#include<functional>
#include<iterator>
#include<random>
#include<unordered_set>
#include<array>
#include<map>
#include<iomanip>
#include<assert.h>
#include<list>
#include<bitset>
#include<stack>
#include<memory>
#include<numeric>
using namespace std;
using namespace std::chrono;
typedef long long int llint;
typedef long double lldo;
#define mp make_pair
#define mt make_tuple
#define pub push_back
#define puf push_front
#define pob pop_back
#define pof pop_front
#define fir first
#define sec second
#define res resize
#define ins insert
#define era erase
/*cout<<fixed<<setprecision(20);cin.tie(0);ios::sync_with_stdio(false);*/
const llint mod=1000000007;
const llint big=2.19e15+1;
const long double pai=3.141592653589793238462643383279502884197;
const long double eps=1e-12;
template <class T,class U>bool mineq(T& a,U b){if(a>b){a=b;return true;}return false;}
template <class T,class U>bool maxeq(T& a,U b){if(a<b){a=b;return true;}return false;}
llint gcd(llint a,llint b){if(a%b==0){return b;}else return gcd(b,a%b);}
llint lcm(llint a,llint b){if(a==0){return b;}return a/gcd(a,b)*b;}
template<class T> void SO(T& ve){sort(ve.begin(),ve.end());}
template<class T> void REV(T& ve){reverse(ve.begin(),ve.end());}
template<class T>llint LBI(const vector<T>&ar,T in){return lower_bound(ar.begin(),ar.end(),in)-ar.begin();}
template<class T>llint UBI(const vector<T>&ar,T in){return upper_bound(ar.begin(),ar.end(),in)-ar.begin();}

int main(void){
	int w,h,K,n,i;cin>>w>>h>>K>>n;
	int H=(h+1)/2,W=(w+1)/2;
	vector<pair<int,int>>dog(n+1);
	dog[n]=mp(mod,mod);
	for(i=0;i<n;i++){cin>>dog[i].sec>>dog[i].fir;}
	SO(dog);
	K-=W;
	if(K<0){cout<<-1<<endl;return 0;}
	pair<int,int>mae=mp(-1,-1);
	int ans=0,dp=0,ep=0,fp=0;
	for(auto it:dog){
		if(mae.fir!=it.fir||mae.sec+6<=it.sec){//清算します
			ans+=min({dp,ep,fp});
			dp=0;ep=0;fp=0;
			if(it.sec==1){dp=99;}
			
		}else{
			for(i=mae.sec+1;i<=it.sec;i++){
				if(i%2==1){int sp=min(dp,ep);dp=fp;ep=sp;fp=sp;}
			}
		}
		if(it.sec%2==0){fp+=2;}//中間
		else{ep++;}
		if(it.sec==w){fp=mod;}
		mae=it;
	}
	//cerr<<"ans="<<ans<<endl;
	cout<<max(0,(H-1)*W-K)+max(0,ans-K)<<endl;
	return 0;
}

