#include<bits/stdc++.h>
using namespace std;
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];
    }
    int dp[n][2]={{0}};
    dp[0][0]=b[0];
    dp[0][1]=a[0];
    for(int i=1;i<n;i++){
        int x=dp[i-1][0]+abs(a[i]-a[i-1])+b[i];
        int y=dp[i-1][1]+abs(a[i]-b[i-1])+b[i];
        int s=dp[i-1][0]+abs(b[i]-a[i-1])+a[i];
        int t=dp[i-1][1]+abs(b[i]-b[i-1])+a[i];
        dp[i][0]=max(x,y);
        dp[i][1]=max(s,t);
    }
    cout<<max(dp[n-1][0],dp[n-1][1]);
    return 0;
}

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