#include<bits/stdc++.h>

using namespace std;

#define ll long long

int main() {
	int n,m; cin >> n >> m;
	ll sum = 0;
	ll mn = 1<<30;

	for(int i = 0;i < n*m;i++) {
		ll tmp;cin>>tmp;
		if (i != 0 && i != n*m-1) mn = min(mn, tmp);
		sum += tmp;
	}
	if (n%2 == 0 && m%2 == 0) cout << sum - mn << endl;
	else cout << sum << endl;
}