#include<bits/stdc++.h>
using namespace std;
const int kMax=1e3+5;
int n,m,a[kMax][kMax],f[kMax][kMax],on[kMax][kMax],un[kMax][kMax];
bool vis[kMax][kMax];
int main(){
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			cin>>a[i][j];
		}
	}
	f[1][1]=a[1][1];
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			on[i][j]=max(on[i+1][j],f[i][j-1]);
			un[i][j]=max(un[i-1][j],f[i][j-1]);
			f[i][j]=max(on[i][j],un[i][j])+a[i][j];
		}
	}
	cout<<f[n][m]<<endl;
	return 0;
}