#include<bits/stdc++.h>
using namespace std;
 
int ans(int a[],int b[],int n,int j){
    if(n==0&&j==0)
        return b[0];
    if(n==0&&j==1)
        return a[0];
    int x=ans(a,b,n-1,0)+b[n]+abs(a[n-1]-a[n]);
    int y=ans(a,b,n-1,1)+b[n]+abs(b[n-1]-a[n]);
    int s=ans(a,b,n-1,0)+a[n]+abs(a[n-1]-b[n]);
    int t=ans(a,b,n-1,1)+a[n]+abs(b[n-1]-b[n]);
    return max(max(x,y),max(s,t));
}
 
int main(){
    int n;
    cin>>n;
    int a[n]={0};
    int b[n]={0};
    for(int i=0;i<n;i++){
        cin>>a[i]>>b[i];
    }
    if(a[0]>b[0])
    	cout<<ans(a,b,n-1,0);
    else cout<<ans(a,b,n-1,1);
    return 0;
}

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