#include <bits/stdc++.h>
using namespace std;

#define rep(i,n) for(int i=0; i<(n); i++)
#define rep2(i,x,n) for(int i=x; i<(n); i++)
#define all(x) x.begin(),x.end()
typedef long long ll;
ll mod = 1000000007;
ll inf = 1e18;
int main(){

    int n,m;
    cin >> n >> m;
    vector<ll> a(n);
    ll aa;
    rep(i,n){
        rep(j,m){
            cin >> aa;
            a[i]+=aa;
        }
    }

    ll x=-1,y=-1;
    ll sum=0;
    rep(i,n-1){
        if(x==-1){
            if(a[i]>a[i+1]) x=a[i];
        }else{
            if(a[i]<a[i+1]) y=a[i];
        }
        if(y!=-1){
            sum+=x-y;
            x=-1;
            y=-1;
            // cout << sum << endl;
        }
    }
    sum+=max(x,a[n-1]);
    cout << sum << endl;
    
    return 0;
}