import java.util.Arrays;
import java.util.Scanner;

class Main {
	public static void main(String[] args) throws Exception {
		new Main().run();
	}

	void run() {
		Scanner sc=new Scanner(System.in);
		int n=2*sc.nextInt();
		int[] a=new int[n];
		for(int i=0;i<n;++i)a[i]=sc.nextInt();
		long ans=-Long.MAX_VALUE/3;
		long[] sum=new long[n];
		for(int i=0;i<n;++i) {
			sum[n-1-i]=(i>0?sum[n-i]:0)+(i%2==0?1:-1)*a[n-1-i];
			
		}
		long cur=0;
		//[0,i)
		for(int i=0;i<=n;++i) {
			if(i%2==0||(n-i)%2==0)
				ans=Math.max(ans,cur+(i<n?sum[i]:0));
			if(i<n)
				cur+=(i%2==0?1:-1)*a[i];
		}
		System.out.println(ans);
	}

	
	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}