//#ifndef fio
//#pragma GCC optimize("Ofast")
//#pragma GCC target("sse3","sse2","sse")
//#pragma GCC target("avx","sse4","sse4.1","sse4.2","ssse3")
//#pragma GCC target("f16c")
//#pragma GCC optimize("inline","fast-math","unroll-loops","no-stack-protector")
//#pragma GCC diagnostic error "-fwhole-program"
//#pragma GCC diagnostic error "-fcse-skip-blocks"
//#pragma GCC diagnostic error "-funsafe-loop-optimizations"
//#pragma GCC diagnostic error "-std=c++20"
//#endif
#include <bits/stdc++.h>
#define N 1000005
#define M 3000005
#define ll long long
#define uint unsigned int
#define ull unsigned long long
#define i128 __int128
#define mk make_pair
#define x first
#define y second
//#define bas 20200721
//#define bas 1000000007
#define ls(x) (x<<1)
#define rs(x) (x<<1|1)
#define VI vector<int>
#define VL vector<ll>
#define lowbit(x) (x&(-x))
#define PII pair<int,int>
#define PLL pair<ll,ll>
#define PIL pair<int,ll>
#define PLI pair<ll,int>
#define PDI pair<double,int>
#define PDD pair<double,double>
#define PVL pair<VI,ll>
#define eps (1e-9)
#define mod 1000000007
//#define double long double
#define int long long
using namespace std;
//int mod=998244353;
const double Pi=acos(-1);
struct mint {
	int x;
	mint() : x(0) {}
	mint(long long y, bool flag = 0) {
		if (flag) x = (int)(y);
		else x = (int)((y % mod + mod) % mod);
	}
	friend const mint ksm(mint a, long long b);
	const mint inv() {return ksm(*this, mod - 2);}
};
bool operator == (const mint a, const mint b) {return a.x == b.x;}
bool operator != (const mint a, const mint b) {return a.x != b.x;}
bool operator <(const mint a,const mint b){return a.x<b.x;}
bool operator >(const mint a,const mint b){return a.x>b.x;}
int operator ! (const mint a) {return !a.x;}
const mint operator + (const mint a, const mint b) {
	mint res(a.x + b.x, 1);
	if (res.x >= mod) res.x -= mod;
	return res;
}
mint& operator += (mint &a, const mint b) {
	a.x += b.x;
	if (a.x >= mod) a.x -= mod;
	return a;
}
const mint operator - (const mint a, const mint b) {
	mint res(a.x - b.x, 1);
	if (res.x < 0) res.x += mod;
	return res;
}
mint& operator -= (mint &a, const mint b) {
	a.x -= b.x;
	if (a.x < 0) a.x += mod;
	return a;
}
const mint operator * (const mint a, const mint b) {
	return mint((long long)a.x * b.x % mod, 1);
}
mint& operator *= (mint &a, const mint b) {
	a.x = (int)((long long)a.x * b.x % mod);
	return a;
}
const mint ksm(mint a, long long b) {
	mint res(1, 1);
	for (; b; a *= a, b >>= 1)
		if (b & 1) res *= a;
	return res;
}
const mint operator / (const mint a, const mint b) {
	return a * ksm(b, mod - 2);
}
mint& operator /= (mint &a, const mint b) {
	a = a * ksm(b, mod - 2);
	return a;
}
ostream& operator << (ostream &out, const mint a) {
	return out << a.x;
}
istream& operator >> (istream &in, mint &a) {
	long long y;
	in >> y, a = mint(y);
	return in;
}
PLL operator +(PLL a,PLL b){
	return mk(a.x+b.x,a.y+b.y);
}
PLL operator +=(PLL &a,const PLL b){
	a=a+b;
	return a;
}
PLL operator *(PLL a,int b){
	a=mk(a.x*b,a.y*b);
	return a;
}
void chkmx(ll &x,ll y){
	x=max(x,y);
}
void chkmn(ll &x,ll y){
	x=min(x,y);
}

int tt;
int n,m,q,k;
string s;
// int a[N];/
PII a[N];
void solve(){	
	cin>>n;
	for(int i=1;i<=n;++i){
		// int x,y;
		cin>>a[i].x>>a[i].y;
	}
	ll ans=a[1].x+a[1].y;
	vector<PII> jj;
	jj.push_back(mk(0,0));
	jj.push_back(mk(a[1].x,a[1].y));
	for(int i=2;i<=n;++i){
		if(jj.back().x<=a[i].x&&jj.back().y<=a[i].y){
			ans+=1ll*a[i].x-jj.back().x+a[i].y-jj.back().y;
			jj.push_back(a[i]);
			continue;
		}
		while(1){
			int x=jj.back().x,y=jj.back().y;
			jj.pop_back();
			int qx=jj.back().x,qy=jj.back().y;
			if(qx<=a[i].x&&qy<=a[i].y){
				int cx,cy;
				cx=min(x,a[i].x);
				cy=min(y,a[i].y);
				jj.push_back(mk(cx,cy));
				ans+=1ll*a[i].x-cx+a[i].y-cy;
				jj.push_back(a[i]);
				break;
			}
		}
	}
	cout<<ans<<'\n';
}
signed main(){
	// freopen("line.in","r",stdin);
	// freopen("line.out","w",stdout);
	ios::sync_with_stdio(false);
	cin.tie(0),cout.tie(0);
	// cin>>tt;
	// while(tt--){
		solve();
		
	// }	
	return 0;
}
/*

*/