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

struct iofast_t {
    iofast_t() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} iofast;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return vector(arg, init);
    else return vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

template <typename Container>
auto distance(const Container &c, decltype(begin(c)) iter) {
    return distance(begin(c), iter);
}

template <typename RIter, typename Compare = less<typename iterator_traits<RIter>::value_type>>
auto isort(RIter first, RIter last, Compare comp = Compare()) {
    vector<int> i(distance(first, last));
    iota(begin(i), end(i), 0);
    sort(begin(i), end(i), [&](auto x, auto y) {
        return comp(*(first + x), *(first + y));
    });
    return i;
}

template <typename, template <typename> typename, typename = void_t<>>
struct detect : false_type {};
template <typename T, template <typename> typename Check>
struct detect<T, Check, void_t<Check<T>>> : true_type {};
template <typename T, template <typename> typename Check>
constexpr inline bool detect_v = detect<T, Check>::value;

template <typename T>
using has_member_sort = decltype(declval<T>().sort());

template <typename Container, typename Compare = less<typename Container::value_type>>
auto sorted(Container c, Compare comp = Compare()) {
    if constexpr (detect_v<Container, has_member_sort>) {
        c.sort(comp);
        return c;
    }
    else {
        sort(begin(c), end(c), comp);
        return c;
    }
}

template <typename Container, typename Compare = equal_to<typename Container::value_type>>
auto uniqued(Container c, Compare comp = Compare()) {
    c.erase(unique(begin(c), end(c), comp), end(c));
    return c;
}

template <typename T, typename Compare = less<T>>
T &chmin(T &l, T r, Compare &&f = less<T>()) { return l = min(l, r, f); }
template <typename T, typename Compare = less<T>>
T &chmax(T &l, T r, Compare &&f = less<T>()) { return l = max(l, r, f); }

template <typename F>
constexpr auto fix(F &&f) noexcept {
    return [f = std::tuple<F>(std::forward<F>(f))](auto &&...args) mutable {
        return std::get<0>(f)(fix(std::get<0>(f)), std::forward<decltype(args)>(args)...);
    };
}

template <typename T>
using pqueue = priority_queue<T, vector<T>, greater<T>>;

int main() {
    constexpr auto inf = INT_MAX / 2;

    constexpr int step[5][2] = {
        { -1, 0 }, { -1, 1 }, { 0, 1 }, { 1, 1 }, { 1, 0 },
    };

    int h, w; cin >> h >> w;

    auto a = vec<int>(-1, h, w);
    for (int i = 1; i < h - 1; ++i) {
        for (int j = 0; j < w; ++j) {
            cin >> a[i][j];
        }
    }

    auto dist = vec<int>(inf, h, w);

    pqueue<array<int, 3>> que;

    for (int i = 0; i < h; ++i) {
        if (a[i][0] < 0) {
            continue;
        }
        que.push({ a[i][0], i, 0 });
        dist[i][0] = a[i][0];
    }

    while (!empty(que)) {
        auto [d, y, x] = que.top(); que.pop();

        if (dist[y][x] < d) {
            continue;
        }

        for (auto [dy, dx] : step) {
            int ny = y + dy;
            int nx = x + dx;

            if (min(ny, nx) < 0 || h <= ny || w <= nx) {
                continue;
            }
            if (a[ny][nx] < 0) {
                continue;
            }

            if (dist[ny][nx] <= d + a[ny][nx]) {
                continue;
            }
            dist[ny][nx] = d + a[ny][nx];

            que.push({ dist[ny][nx], ny, nx });
        }
    }

    int ans = inf;
    for (int i = 0; i < h; ++i) {
        chmin(ans, dist[i][w - 1]);
    }

    if (ans != inf) {
        cout << ans << endl;
    }
    else {
        cout << -1 << endl;
    }
}