#define _GLIBCXX_DEBUG
#include<bits/stdc++.h>
#include<atcoder/all>
#define rep(i,b) for(int i=0;i<b;i++)
#define rrep(i,b) for(int i=b-1;i>=0;i--)
#define rep1(i,b) for(int i=1;i<b;i++)
#define repx(i,x,b) for(int i=x;i<b;i++)
#define rrepx(i,x,b) for(int i=b-1;i>=x;i--)
#define fore(i,a) for(auto i:a)
#define fore1(i,a) for(auto &i:a)
#define rng(x) (x).begin(), (x).end()
#define rrng(x) (x).rbegin(), (x).rend()
#define sz(x) ((int)(x).size())
#define pb push_back
#define fi first
#define se second
#define pcnt __builtin_popcountll

using namespace std;
using namespace atcoder;

using ll = long long;
using ld = long double;
template<typename T> using mpq = priority_queue<T, vector<T>, greater<T>>;
template<typename T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<typename T> bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
template<typename T> ll sumv(const vector<T>&a){ll res(0);for(auto&&x:a)res+=x;return res;}
bool yn(bool a) { if(a) {cout << "Yes" << endl; return 1;} else {cout << "No" << endl; return 0;}}
#define dame { cout << "No" << endl; return 0;}
#define dame1 { cout << -1 << endl; return 0;}
#define test(x) cout << "test" << x << endl;
#define deb(x,y) cout << x << " " << y << endl;
#define debp(p) cout << p.fi << " " << p.se << endl;
#define deb3(x,y,z) cout << x << " " << y << " " << z << endl;
#define deb4(x,y,z,x2) cout << x << " " << y << " " << z << " " << x2 << endl;
#define out cout << ans << endl;
#define outd cout << fixed << setprecision(20) << ans << endl;
#define outm cout << ans.val() << endl;
#define outv fore(yans , ans) cout << yans << "\n";
#define outdv fore(yans , ans) cout << yans.val() << "\n";
#define show(x) cerr<<#x<<" = "<<x<<endl;
#define showdeb(x,y) cerr<<#x<<" = "<<x<<" : "<<#y<<" = "<<y<<endl;
#define showv(v) {fore(vy , v) {cout << vy << " ";} cout << endl;}
#define showv2(v) fore(vy , v) cout << vy << "\n";
#define showvm(v) {fore(vy , v) {cout << vy.val() << " ";} cout << endl;}
#define showvm2(v) fore(vy , v) cout << vy.val() << "\n";
using pll = pair<ll,ll>;using pil = pair<int,ll>;using pli = pair<ll,int>;using pii = pair<int,int>;using pdd = pair<ld,ld>;
using tp = tuple<int ,int ,int>;
using vi = vector<int>;using vd = vector<ld>;using vl = vector<ll>;using vs = vector<string>;using vb = vector<bool>;
using vpii = vector<pii>;using vpli = vector<pli>;using vpll = vector<pll>;using vpil = vector<pil>;
using vvi = vector<vector<int>>;using vvl = vector<vector<ll>>;using vvs = vector<vector<string>>;using vvb = vector<vector<bool>>;
using vvpii = vector<vector<pii>>;using vvpli = vector<vector<pli>>;using vvpll = vector<vpll>;using vvpil = vector<vpil>;
using mint = modint998244353;
using vm = vector<mint>;
using vvm = vector<vector<mint>>;
vector<int> dx={1,0,-1,0,1,1,-1,-1},dy={0,1,0,-1,1,-1,1,-1};
ll gcd(ll a, ll b) { return a?gcd(b%a,a):b;}
ll lcm(ll a, ll b) { return a/gcd(a,b)*b;}
#define yes {cout <<"Yes"<<endl;}
#define yesr { cout <<"Yes"<<endl; return 0;}
#define no {cout <<"No"<<endl;}
#define nor { cout <<"No"<<endl; return 0;}
const double eps = 1e-10;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;

struct state{
    int i,j,t;
 
    state(int i=0,int j=0,int t=0) : i(i),j(j),t(t) {}
 
    bool operator<(state const &ot) const{
        return i < ot.i;
    }
};

using pp = pair<ll , state>;

void solve(){
    int n,m; cin>>n>>m;

    vvl a(n,vl(m));
    rep(i,n) rep(j,m) cin>>a[i][j];

    vector<vvl> dist(n,vvl(m,vl(2,LINF)));
    mpq<pp> q;
    
    state st(0,0,1);
    dist[st.i][st.j][st.t] = 0;
    q.push({dist[st.i][st.j][st.t] , st});

    // t = 0が下から
    
    while(!q.empty()){
        pp p = q.top();
        q.pop();
        ll dist_dum = p.first;
        state f = p.second;
    
        if (dist[f.i][f.j][f.t] < dist_dum) continue;

        int ni=f.i,nj=f.j,nt=f.t;
        ll cost=0;
    
        if (f.j > 0){
            nj--;
            nt = 1;
            if (chmin(dist[ni][nj][nt] , dist_dum)){
                pp nxt = {dist[ni][nj][nt] , state(ni,nj,nt)};
                q.push(nxt);
            }
        }

        if (f.j < m-1){
            nj = f.j+1;
            nt = 1;
            if (chmin(dist[ni][nj][nt] , dist_dum)){
                pp nxt = {dist[ni][nj][nt] , state(ni,nj,nt)};
                q.push(nxt);
            }
        }

        if (f.i < n-1){
            ni = f.i+1;
            nj = f.j;
            nt = 0;
            if (f.t == 1) cost = a[f.i][f.j];
            cost += a[ni][nj];
            if (chmin(dist[ni][nj][nt] , dist_dum+cost)){
                pp nxt = {dist[ni][nj][nt] , state(ni,nj,nt)};
                q.push(nxt);
            }
        }
    }

    ll ans = LINF;

    rep(j,m) rep(t,2) chmin(ans , dist[n-1][j][t]);

    out;
    
    return;
}

int main(){

    solve();

    return 0;
}