import java.util.Scanner;


public class Beans {
    static int a[] = new int[200010], dp[] = new int[200010], DP[] = new int[200010], b[] = new int[200010];
    public static void main(String[] argvs){
        int M, N;
        Scanner cin = new Scanner(System.in);
        while(cin.hasNext()){
            M = cin.nextInt();
            N = cin.nextInt();
            for(int i = 0; i < M; i++){
                DP[i] = 0;
                for(int j = 0; j < N; j++){
                    dp[j] = 0;
                    a[j] = cin.nextInt();
                    if(j < 2)
                        dp[j] = a[j];
                    else 
                        dp[j] = Math.max(dp[j - 2] + a[j], dp[j - 1]);
                }
                DP[i] = dp[N - 1];
                if(i < 2)
                    b[i] = DP[i];
                else
                    b[i] = Math.max(b[i - 2] + DP[i], b[i - 1]);
            }
            System.out.println(b[M - 1]);
        }
        
    }
}