#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <complex>
#include <deque>
#include <forward_list>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <optional>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
using lint = long long;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(nullptr), ios::sync_with_stdio(false), cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template <typename T> bool chmax(T &m, const T q) { return m < q ? (m = q, true) : false; }
template <typename T> bool chmin(T &m, const T q) { return m > q ? (m = q, true) : false; }
const std::vector<std::pair<int, int>> grid_dxs{{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
int floor_lg(long long x) { return x <= 0 ? -1 : 63 - __builtin_clzll(x); }
template <class T1, class T2> T1 floor_div(T1 num, T2 den) { return (num > 0 ? num / den : -((-num + den - 1) / den)); }
template <class T1, class T2> std::pair<T1, T2> operator+(const std::pair<T1, T2> &l, const std::pair<T1, T2> &r) { return std::make_pair(l.first + r.first, l.second + r.second); }
template <class T1, class T2> std::pair<T1, T2> operator-(const std::pair<T1, T2> &l, const std::pair<T1, T2> &r) { return std::make_pair(l.first - r.first, l.second - r.second); }
template <class T> std::vector<T> sort_unique(std::vector<T> vec) { sort(vec.begin(), vec.end()), vec.erase(unique(vec.begin(), vec.end()), vec.end()); return vec; }
template <class T> int arglb(const std::vector<T> &v, const T &x) { return std::distance(v.begin(), std::lower_bound(v.begin(), v.end(), x)); }
template <class T> int argub(const std::vector<T> &v, const T &x) { return std::distance(v.begin(), std::upper_bound(v.begin(), v.end(), x)); }
template <class IStream, class T> IStream &operator>>(IStream &is, std::vector<T> &vec) { for (auto &v : vec) is >> v; return is; }

template <class OStream, class T> OStream &operator<<(OStream &os, const std::vector<T> &vec);
template <class OStream, class T, size_t sz> OStream &operator<<(OStream &os, const std::array<T, sz> &arr);
template <class OStream, class T, class TH> OStream &operator<<(OStream &os, const std::unordered_set<T, TH> &vec);
template <class OStream, class T, class U> OStream &operator<<(OStream &os, const pair<T, U> &pa);
template <class OStream, class T> OStream &operator<<(OStream &os, const std::deque<T> &vec);
template <class OStream, class T> OStream &operator<<(OStream &os, const std::set<T> &vec);
template <class OStream, class T> OStream &operator<<(OStream &os, const std::multiset<T> &vec);
template <class OStream, class T> OStream &operator<<(OStream &os, const std::unordered_multiset<T> &vec);
template <class OStream, class T, class U> OStream &operator<<(OStream &os, const std::pair<T, U> &pa);
template <class OStream, class TK, class TV> OStream &operator<<(OStream &os, const std::map<TK, TV> &mp);
template <class OStream, class TK, class TV, class TH> OStream &operator<<(OStream &os, const std::unordered_map<TK, TV, TH> &mp);
template <class OStream, class... T> OStream &operator<<(OStream &os, const std::tuple<T...> &tpl);

template <class OStream, class T> OStream &operator<<(OStream &os, const std::vector<T> &vec) { os << '['; for (auto v : vec) os << v << ','; os << ']'; return os; }
template <class OStream, class T, size_t sz> OStream &operator<<(OStream &os, const std::array<T, sz> &arr) { os << '['; for (auto v : arr) os << v << ','; os << ']'; return os; }
template <class... T> std::istream &operator>>(std::istream &is, std::tuple<T...> &tpl) { std::apply([&is](auto &&... args) { ((is >> args), ...);}, tpl); return is; }
template <class OStream, class... T> OStream &operator<<(OStream &os, const std::tuple<T...> &tpl) { os << '('; std::apply([&os](auto &&... args) { ((os << args << ','), ...);}, tpl); return os << ')'; }
template <class OStream, class T, class TH> OStream &operator<<(OStream &os, const std::unordered_set<T, TH> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <class OStream, class T> OStream &operator<<(OStream &os, const std::deque<T> &vec) { os << "deq["; for (auto v : vec) os << v << ','; os << ']'; return os; }
template <class OStream, class T> OStream &operator<<(OStream &os, const std::set<T> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <class OStream, class T> OStream &operator<<(OStream &os, const std::multiset<T> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <class OStream, class T> OStream &operator<<(OStream &os, const std::unordered_multiset<T> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <class OStream, class T, class U> OStream &operator<<(OStream &os, const std::pair<T, U> &pa) { return os << '(' << pa.first << ',' << pa.second << ')'; }
template <class OStream, class TK, class TV> OStream &operator<<(OStream &os, const std::map<TK, TV> &mp) { os << '{'; for (auto v : mp) os << v.first << "=>" << v.second << ','; os << '}'; return os; }
template <class OStream, class TK, class TV, class TH> OStream &operator<<(OStream &os, const std::unordered_map<TK, TV, TH> &mp) { os << '{'; for (auto v : mp) os << v.first << "=>" << v.second << ','; os << '}'; return os; }
#ifdef HITONANODE_LOCAL
const string COLOR_RESET = "\033[0m", BRIGHT_GREEN = "\033[1;32m", BRIGHT_RED = "\033[1;31m", BRIGHT_CYAN = "\033[1;36m", NORMAL_CROSSED = "\033[0;9;37m", RED_BACKGROUND = "\033[1;41m", NORMAL_FAINT = "\033[0;2m";
#define dbg(x) std::cerr << BRIGHT_CYAN << #x << COLOR_RESET << " = " << (x) << NORMAL_FAINT << " (L" << __LINE__ << ") " << __FILE__ << COLOR_RESET << std::endl
#define dbgif(cond, x) ((cond) ? std::cerr << BRIGHT_CYAN << #x << COLOR_RESET << " = " << (x) << NORMAL_FAINT << " (L" << __LINE__ << ") " << __FILE__ << COLOR_RESET << std::endl : std::cerr)
#else
#define dbg(x) ((void)0)
#define dbgif(cond, x) ((void)0)
#endif

template <typename T> std::vector<std::vector<T>> transpose(const std::vector<std::vector<T>> &v) {
    const int H = v.size(), W = v[0].size();
    std::vector<std::vector<T>> ret(W, std::vector<T>(H));
    for (int i = 0; i < H; i++) {
        for (int j = 0; j < W; j++) ret[j][i] = v[i][j];
    }
    return ret;
}

std::vector<std::string> transpose(const std::vector<std::string> &v) {
    const int H = v.size(), W = v[0].size();
    std::vector<std::string> ret(W, std::string(H, '\0'));
    for (int i = 0; i < H; i++) {
        for (int j = 0; j < W; j++) ret[j][i] = v[i][j];
    }
    return ret;
}

void answer(int x) {
    cout << x << '\n';
    exit(0);
}

int main() {
    int H, W;
    cin >> H >> W;
    vector A(H, vector<int>(W));
    cin >> A;
    dbg(A);
    // REP(_, 2) {
    //     for (size_t i = 0; i < A.size();) {
    //         if (accumulate(ALL(A.at(i)), 0) == 0) {
    //             A.erase(A.begin() + i);
    //         } else {
    //             ++i;
    //         }
    //     }
    //     A = transpose(A);
    // }
    // dbg(A);

    // if (A.empty() or A.front().empty()) answer(0);

    // H = A.size(), W = A.front().size();

    vector<int> i2maxj(H, -1), j2maxi(W, -1);

    REP(i, H) REP(j, W) {
        if (A.at(i).at(j) == 1) {
            chmax(i2maxj.at(i), j);
            chmax(j2maxi.at(j), i);
        }
    }

    vector cs(H + 1, vector<int>(W + 1));
    REP(i, H) REP(j, W) {
        cs.at(i + 1).at(j + 1) = cs.at(i + 1).at(j) + cs.at(i).at(j + 1) - cs.at(i).at(j) + A.at(i).at(j);
    }
    dbg(i2maxj);
    dbg(j2maxi);

    // [ilo, ihi) * [jlo, jhi)
    auto sum = [&](int ilo, int ihi, int jlo, int jhi) {
        return cs.at(ihi).at(jhi) - cs.at(ilo).at(jhi) - cs.at(ihi).at(jlo) + cs.at(ilo).at(jlo);
    };

    constexpr int inf = 1 << 27;
    vector dp(H, vector<int>(W, inf));

    IREP(x, H) IREP(y, W) {
        int nin = sum(x, H, y, W);
        if (!nin) {
            dp.at(x).at(y) = 0;
            continue;
        }

        vector<int> xin(H);
        FOR(i, x, H) xin.at(i) = sum(i, i + 1, y, W) > 0;
        vector<int> xin_cs(H + 1);
        REP(i, H) xin_cs.at(i + 1) = xin_cs.at(i) + xin.at(i);

        vector<int> yin(W);
        FOR(j, y, W) yin.at(j) = sum(x, H, j, j + 1) > 0;
        vector<int> yin_cs(W + 1);
        REP(j, W) yin_cs.at(j + 1) = yin_cs.at(j) + yin.at(j);

        vector<int> x2yhi = i2maxj;
        IFOR(i, 1, H) chmax(x2yhi.at(i - 1), x2yhi.at(i));
        // FOR(i, x, H) {
        //     const int j = i2maxj.at(i);
        //     if (j < y) continue;
        //     while (x2y.size() and x2y.back().second <= y) x2y.pop_back();
        //     x2y.emplace_back(i, j);
        // }
        FOR(i, x, H) {
            // for (auto [i, j] : x2y) {
            const int j = x2yhi.at(i);
            int s = (xin_cs.at(i + 1) - xin_cs.at(x)) * (yin_cs.at(j + 1) - yin_cs.at(y));
            if (i < H - 1) s += dp.at(i + 1).at(y);
            if (j < W - 1) s += dp.at(x).at(j + 1);
            chmin(dp.at(x).at(y), s);
        }

        // if (y + 1 < W and !sum(x, H, y, y + 1)) chmin(dp.at(x).at(y), dp.at(x).at(y + 1));
        // if (x + 1 < H and !sum(x, x + 1, y, W)) chmin(dp.at(x).at(y), dp.at(x + 1).at(y));
    }

    for (auto v : dp) dbg(v);

    int init = 0;
    for (auto v : A) init += accumulate(ALL(v), 0);

    cout << dp.at(0).at(0) - init << '\n';
}