#include<bits/stdc++.h>
using namespace std;
#ifdef DEBUG
#include"debug.h"
#else
#define debug(...) void()
#endif
#define all(x) (x).begin(),(x).end()
template<class T>
auto ary(T *a,int l,int r){
	return vector<T>{a+l,a+1+r};
}
using ll=long long;
using ull=unsigned ll;
const int N=2e5+10,M=N*2;
int n;
struct node{
	int x,y;
}a[N];
ll cross(node a,node b){
	return 1ll*a.x*b.y-1ll*a.y*b.x;
}
vector<int>nx,ny;
using vec=array<int,4>;
#ifdef DEBUG
ostream& operator << (ostream &out,vec a){
	out<<'[';
	for(auto x:a)out<<x<<',';
	return out<<']';
}
#endif
namespace SGT1{
	const vec I={0,1,2,3};
	vec operator + (const vec &a,const vec &b){
		static vec c;
		for(int i=0;i<4;i++)c[i]=a[i]+b[i];
		return c;
	}
	vec merge(const vec &a,const vec &b){
		static vec c;
		for(int i=0;i<4;i++)c[i]=b[a[i]];
		return c;
	}
	vec Merge(const vec &a,const vec &b){
		static vec c;
		c.fill(0);
		for(int i=0;i<4;i++)c[b[i]]+=a[i];
		return c;
	}
	vec t[M<<2],laz[M<<2];
	void pushup(int rt){
		t[rt]=t[rt<<1]+t[rt<<1|1];
	}
	void pushlaz(int rt,vec x){
		t[rt]=Merge(t[rt],x);
		laz[rt]=merge(laz[rt],x);
	}
	void pushdown(int rt){
		if(laz[rt]!=I){
			pushlaz(rt<<1,laz[rt]);
			pushlaz(rt<<1|1,laz[rt]);
			laz[rt]=I;
		}
	}
	void build(int l=0,int r=ny.size()-2,int rt=1){
		laz[rt]=I;
		if(l==r)return t[rt][0]=ny[l+1]-ny[l],void();
		int mid=(l+r)>>1;
		build(l,mid,rt<<1);
		build(mid+1,r,rt<<1|1);
		pushup(rt);
	}
	void update(int L,int R,vec x,int l=0,int r=ny.size()-2,int rt=1){
		// if(rt==1)debug("update",L,R,x);
		if(L<=l&&r<=R)return pushlaz(rt,x);
		int mid=(l+r)>>1;
		pushdown(rt);
		if(L<=mid)update(L,R,x,l,mid,rt<<1);
		if(mid<R)update(L,R,x,mid+1,r,rt<<1|1);
		pushup(rt);
	}
	vec query(int L=0,int R=ny.size()-2,int l=0,int r=ny.size()-2,int rt=1){
		if(L<=l&&r<=R)return t[rt];
		int mid=(l+r)>>1;
		pushdown(rt);
		if(R<=mid)return query(L,R,l,mid,rt<<1);
		if(mid<L)return query(L,R,mid+1,r,rt<<1|1);
		return query(L,R,l,mid,rt<<1)+query(L,R,mid+1,r,rt<<1|1);
	}
}
namespace SGT2{
	struct node{
		int st,ed,cnt;
		bool f,g;
	};
	node operator + (const node &a,const node &b){
		if(a.st==-1)return b;
		if(b.st==-1)return a;
		if(a.cnt%2==0)return {a.st,b.ed,a.cnt+b.cnt,a.f&&b.f,a.g&&b.g&&(b.st-a.ed)%2==0};
		else return {a.st,b.ed,a.cnt+b.cnt,a.f&&b.g&&(b.st-a.ed)%2==0,a.g&&b.f};
	}
	node t[M<<2];
	void pushup(int rt){
		t[rt]=t[rt<<1]+t[rt<<1|1];
	}
	void build(int l=0,int r=ny.size()-1,int rt=1){
		t[rt]={-1,-1,0,0,0};
		if(l==r)return;
		int mid=(l+r)>>1;
		build(l,mid,rt<<1);
		build(mid+1,r,rt<<1|1);
	}
	void update(int x,int l=0,int r=ny.size()-1,int rt=1){
		if(l==r){
			if(t[rt].st==-1)t[rt]={ny[l],ny[l],1,1,1};
			else t[rt]={-1,-1,0,0,0};
			return;
		}
		int mid=(l+r)>>1;
		if(x<=mid)update(x,l,mid,rt<<1);
		else update(x,mid+1,r,rt<<1|1);
		pushup(rt);
	}
	bool query(){
		return t[1].f;
	}
}
vector<pair<int,int>>o1[M],o2[M];
void reduce(vector<pair<int,int>>&o){
	sort(all(o));
	int len=-1;
	for(int i=0;i<len;i++){
		if(len==-1||o[len].second!=o[i].first)o[++len]=o[i];
		else o[len].second=o[i].second;
	}
	o.resize(len+1);
}
int main(){
	scanf("%d%*d",&n);
	for(int i=1;i<=n;i++){
		scanf("%d%d",&a[i].x,&a[i].y);
	}
	if([&](){
		ll s=0;
		for(int i=1;i<=n;i++){
			s+=cross(a[i],a[i%n+1]);
		}
		return s<0;
	}())reverse(a+1,a+1+n);
	for(int i=1;i<=n;i++){
		nx.push_back(a[i].x);
		ny.push_back(a[i].y);
	}
	sort(all(nx)),nx.erase(unique(all(nx)),nx.end());
	sort(all(ny)),ny.erase(unique(all(ny)),ny.end());
	for(int i=1;i<=n;i++){
		a[i].x=lower_bound(all(nx),a[i].x)-nx.begin();
		a[i].y=lower_bound(all(ny),a[i].y)-ny.begin();
	}
	for(int i=1;i<=n;i++){
		int j=i%n+1;
		if(a[i].x!=a[j].x)continue;
		if(a[i].y>a[j].y){
			o1[a[i].x].push_back({a[j].y,a[i].y});
		}else{
			o2[a[i].x].push_back({a[i].y,a[j].y});
		}
	}
	int ans=0;
	SGT1::build();
	SGT2::build();
	// debug(nx,ny);
	for(int i=0;i+1<nx.size();i++){
		if(![&](){
			reduce(o1[i]);
			reduce(o2[i]);
			for(auto [l,r]:o1[i]){
				auto res=SGT1::query(l,r-1);
				SGT1::update(l,r-1,vec({1,1,3,3}));
				SGT2::update(l),SGT2::update(r);
				if((res[2]||res[3])&&!SGT2::query())return 0;
			}
			for(auto [l,r]:o2[i]){
				auto res=SGT1::query(l,r-1);
				if(res[2]||res[3])return 0;
				SGT1::update(l,r-1,vec({0,0,2,2}));
				SGT2::update(l),SGT2::update(r);
			}
			if(!SGT2::query())return 0;
			int d=nx[i+1]-nx[i];
			static vec t={0,3,2,1};
			if(d%2==0)SGT1::update(0,ny.size()-2,t);
			auto res=SGT1::query();
			// debug(i,res);
			if(!res[2]&&!res[3])ans=nx[i+1]-1;
			SGT1::update(0,ny.size()-2,t);
			res=SGT1::query();
			// debug(i,res);
			if(!res[2]&&!res[3])ans=nx[i+1];
			return 1;
		}())break;
	}
	cout<<ans<<endl;
	return 0;
}
#ifdef DEBUG
#include"debug.hpp"
#endif