import std;

// 構造体のままダイクストラ(ただし、重みはメンバ変数として管理)を試してみる

struct node {
    int y;
    int x;
    int weight;
}

void main () {
    // input
    int H, W; readln.read(H, W);
    int[][] A = new int[][](H-2, 0);
    foreach (i; 0..H-2) {
        A[i] = 0 ~ readln.split.to!(int[]);
    }

    // グラフ構築
    int[] dxy = [-1, 0, 1];
    node[][][] graph = new node[][][](H-2, W+1, 0);
    foreach (i; 0..H-2) {
        foreach (j; 0..W+1) {

            // 8方向に辺を張る
            foreach (dy; dxy) {
                foreach (dx; dxy) {
                    if (dy == 0 && dx == 0) {
                        continue;
                    }
                    if (H-2 <= i+dy || W+1 <= j+dx || i+dy < 0 || j+dx < 0) {
                        continue;
                    }
                    if (A[i+dy][j+dx] == -1) {
                        continue;
                    }
                    graph[i][j] ~= node(i+dy, j+dx, A[i+dy][j+dx]);
                }
            }
        }
    }

    solve(H, W, A, graph);
}

struct toNode {
    int y;
    int x;
    int totalCost;
}

void solve (int H, int W, int[][] A, node[][][] graph) {
    int[][] comfirmedCost = new int[][](H-2, W+1);
    foreach (ref c; comfirmedCost) {
        c[] = int.max;
    }
    BinaryHeap!(Array!toNode, "a.totalCost > b.totalCost") PQ;

    // 最初の一列はタダで張れるので、最初の一列のどこかを確定頂点にする
    PQ.insert(toNode(0, 0, 0));

    int count = 0;
    int all = 0;
    while (!PQ.empty) {
        all++;
        auto shortest = PQ.front; PQ.removeFront;
        if (comfirmedCost[shortest.y][shortest.x] < shortest.totalCost) {
            count++;
            continue;
        }

        comfirmedCost[shortest.y][shortest.x] = shortest.totalCost;
        // 新しく追加された確定頂点から候補を伸ばす
        foreach (to; graph[shortest.y][shortest.x]) {
            if (to.weight + shortest.totalCost < comfirmedCost[to.y][to.x]) {
                PQ.insert(toNode(to.y, to.x, to.weight + shortest.totalCost));
                comfirmedCost[to.y][to.x] = to.weight + shortest.totalCost;
            }
        }
    }
    writeln("count = ", count);
    writeln("all = ", all);

    // 端に到達できたかチェック
    int ans = int.max;
    foreach (i; 0..H-2) {
        ans = min(ans, comfirmedCost[i][W]);
    }

    if (ans == int.max) {
        writeln(-1);
    } else {
        writeln(ans);
    }
}

void read(T...)(string S, ref T args) {
    auto buf = S.split;
    foreach (i, ref arg; args) {
        arg = buf[i].to!(typeof(arg));
    }
}