import java.io.*;
import java.util.*;
import java.util.function.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int[][] dp = new int[n][2];
        dp[0][0] = sc.nextInt();
        dp[0][1] = sc.nextInt();
        for (int i = 1; i < n; i++) {
            int p = sc.nextInt();
            int a = sc.nextInt();
            dp[i][0] = Math.max(dp[i - 1][0], dp[i - 1][1] + p) + p;
            dp[i][1] = Math.max(dp[i - 1][0], dp[i - 1][1] + a) + a;
        }
        System.out.println(dp[n - 1][0]);
    }
}
class Scanner {
    BufferedReader br;
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() {
        try {
            br = new BufferedReader(new InputStreamReader(System.in));
        } catch (Exception e) {
            
        }
    }
    
    public int nextInt() {
        return Integer.parseInt(next());
    }
    
    public long nextLong() {
        return Long.parseLong(next());
    }
    
    public double nextDouble() {
        return Double.parseDouble(next());
    }
    
    public String next() {
        try {
            while (!st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            return st.nextToken();
        }
    }
    
}