#include <bits/stdc++.h>

using namespace std;
#define SZ(x) (int) (x).size()
#define REP(i, n) for(int i = 0; i < (n); i++)
#define FOR(i, a, b) for(auto i = (a); i < (b); i++)
#define For(i, a, b, c) \
	for(auto i = (a); i != (b); i += (c))
#define REPR(i, n) for(auto i = (n) -1; i >= 0; i--)
#define ALL(s) (s).begin(), (s).end()
#define so(V) sort(ALL(V))
#define rev(V) reverse(ALL(V))
#define uni(v) v.erase(unique(ALL(v)), (v).end())
#define eb emplace_back

typedef unsigned long long ull;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<bool> vb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> PI;
typedef pair<ll, ll> PL;
const double EPS = 1e-6;
const int MOD = 1e9 + 7;
const int INF = (1 << 30);
const ll LINF = 1e18;
const double math_PI = acos(-1);

template<typename T>
vector<T> make_v(size_t a) {
	return vector<T>(a);
}

template<typename T, typename... Ts>
auto make_v(size_t a, Ts... ts) {
	return vector<decltype(make_v<T>(ts...))>(
		a, make_v<T>(ts...));
}

template<typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill_v(
	T& t, const V& v) {
	t = v;
}

template<typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill_v(
	T& t, const V& v) {
	for(auto& e: t) fill_v(e, v);
}

template<class T>
bool chmax(T& a, const T& b) {
	if(a < b) {
		a = b;
		return true;
	}
	return false;
}

template<class T>
bool chmin(T& a, const T& b) {
	if(a > b) {
		a = b;
		return true;
	}
	return false;
}

template<typename S, typename T>
istream& operator>>(istream& is, pair<S, T>& p) {
	cin >> p.first >> p.second;
	return is;
}

template<typename T>
istream& operator>>(istream& is, vector<T>& vec) {
	for(T& x: vec) is >> x;
	return is;
}

template<typename T>
string join(vector<T>& vec, string splitter) {
	stringstream ss;
	REP(i, SZ(vec)) {
		if(i != 0) ss << splitter;
		ss << vec[i];
	}
	return ss.str();
}

template<typename T>
ostream& operator<<(ostream& os, vector<T>& vec) {
	os << join(vec, " ");
	return os;
}
template<typename T>
struct RangeSum {
private:
	vector<T> V;
	int N = -1;

public:
	RangeSum(vector<T> &v) {
		N = SZ(v);
		V = vector<T>(N + 1);
		V[0] = T(0);
		REP(i, N) {
			V[i + 1] = v[i] + V[i];
		}
	}

	T sum(int l, int r) {
		chmax(l, 0);
		chmin(r, N);
		chmax(r, l);
		return V[r] - V[l];
	}
};

template<typename T>
struct RangeSum2D {
private:
	vector<vector<T>> V;
	int H = -1;
	int W = -1;

public:
	RangeSum2D(vector<vector<T>> &v) {
		H = SZ(v);
		W = SZ(v[0]);
		V = vector<vector<T>>(H, vector<T>(W));
		REP(i, H) {
			REP(j, W) {
				V[i][j] += v[i][j];
				if(i != 0) V[i][j] += V[i - 1][j];
				if(j != 0) V[i][j] += V[i][j - 1];
				if(i != 0 && j != 0)
					V[i][j] -= V[i - 1][j - 1];
			}
		}
	}

	T sum(int y1, int x1, int y2, int x2) {
		T ret = V[y2][x2];
		if(y1 != 0) ret -= V[y1 - 1][x2];
		if(x1 != 0) ret -= V[y2][x1 - 1];
		if(y1 != 0 && x1 != 0) ret += V[y1 - 1][x1 - 1];
		return ret;
	}
};

int main() {
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	int H, W;
	cin >> H >> W;
	vvi A(H - 2, vi(W));
	cin >> A;
	vvll T(W, vll(H - 2));
	REP(i, H - 2) {
		REP(j, W) {
			T[j][i] = A[i][j];
			if(A[i][j] == -1) {
				T[j][i] = INF;
			}
		}
	}
	auto dp = make_v<ll>(W, H - 2);
	fill_v(dp, INF);
	REP(j, H - 2) dp[0][j] = T[0][j];

	REP(i, W - 1) {
		RangeSum<ll> RS(T[i + 1]);
		REP(j, H - 2) {
			REP(k, H - 2) {
				if(j == k) {
					chmin(dp[i + 1][k],
						  dp[i][j] + T[i + 1][k]);
				} else if(j > k) {
					chmin(dp[i + 1][k],
						  dp[i][j] + RS.sum(k, j));
				} else {
					chmin(dp[i + 1][k],
						  dp[i][j] + RS.sum(j + 1, k + 1));
				}
			}
		}
	}
	ll ans = INF;
	REP(i, H - 2) {
		chmin(ans, dp[W - 1][i]);
	}
	if(ans >= INF) {
		cout << -1 << endl;
	} else {
		cout << ans << endl;
	}
	return 0;
}