#include <iostream>
#include <cassert>
#include <queue>
using namespace std;
typedef long long ll;

template <typename T = int>
struct edge
{
    int from, to;
    T cost;
    int id;

    operator int() const
    {
        return to;
    }
};

template <typename T = int>
struct graph
{
    int n, m;
    std::vector<std::vector<edge<T>>> g;

    graph() {}

    graph(int n) : n(n), m(0)
    {
        g.resize(n);
    }

    void add_directed_edge(int from, int to, T cost = 1)
    {
        assert(0 <= from && from < n);
        assert(0 <= to && to < n);
        g[from].push_back((edge<T>){from, to, cost, m++});
    }

    void add_undirected_edge(int from, int to, T cost = 1)
    {
        assert(0 <= from && from < n);
        assert(0 <= to && to < n);
        g[from].push_back((edge<T>){from, to, cost, m});
        g[to].push_back((edge<T>){to, from, cost, m++});
    }

    int size()
    {
        return n;
    }

    int edge_size()
    {
        return m;
    }

    inline const std::vector<edge<T>> &operator[](const int &u) const
    {
        return g[u];
    }

    inline std::vector<edge<T>> &operator[](const int &u)
    {
        return g[u];
    }
};

template <typename T = long long, typename G>
std::vector<T> dijkstra(G &g, int s)
{
    using P = std::pair<T, int>;
    int n = g.size();
    assert(s >= 0 && s < n);
    std::vector<T> d(n, -1);
    std::priority_queue<P, std::vector<P>, std::greater<P>> que;
    d[s] = 0;
    que.push(P(0, s));
    while (que.size())
    {
        auto [dist, u] = que.top();
        que.pop();
        if (d[u] < dist)
        {
            continue;
        }
        for (edge<T> e : g[u])
        {
            int v = e.to;
            if (d[v] == -1 || d[v] > d[u] + e.cost)
            {
                d[v] = d[u] + e.cost;
                que.push(P(d[v], v));
            }
        }
    }
    return d;
}

int a[1005][1005];

int main()
{
    int n, m;
    cin >> n >> m;
    for(int i = 0; i < n; i++)
    {
        for(int j = 0; j < m; j++)
        {
            cin >> a[i][j];
        }
    }
    graph<ll> g(n * m + n);
    for(int i = 0; i < n; i++)
    {
        for(int j = 0; j < m; j++)
        {
            g.add_directed_edge(i * m + j, i + n * m, 0);
        }
    }
    for(int i = 0; i < n - 1; i++)
    {
        for(int j = 0; j < m; j++)
        {
            g.add_directed_edge(i + n * m, (i + 1) * m + j, a[i][j] + a[i + 1][j]);
            g.add_directed_edge(i * m + j, (i + 1) * m + j, a[i + 1][j]);
        }
    }
    vector<ll> d = dijkstra(g, n * m);
    cout << d[n * m + n - 1] << endl;
}