#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <chrono>
#include <complex>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <unordered_map>
#include <vector>

using namespace std;

// BEGIN NO SAD
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define trav(a, x) for(auto& a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
typedef vector<int> vi;
#define f first
#define s second
#define derr if(0) cerr
void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ", "; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? ", " : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#define debug(x...) cerr << "\e[91m"<<__func__<<":"<<__LINE__<<" [" << #x << "] = ["; _print(x); cerr << "\e[39m" << flush;
// END NO SAD

template<class Fun>
class y_combinator_result {
  Fun fun_;
public:
  template<class T>
  explicit y_combinator_result(T &&fun): fun_(std::forward<T>(fun)) {}

  template<class ...Args>
  decltype(auto) operator()(Args &&...args) {
    return fun_(std::ref(*this), std::forward<Args>(args)...);
  }
};

template<class Fun>
decltype(auto) y_combinator(Fun &&fun) {
  return y_combinator_result<std::decay_t<Fun>>(std::forward<Fun>(fun));
}

template<class T>
bool updmin(T& a, T b) {
  if(b < a) {
    a = b;
    return true;
  }
  return false;
}
template<class T>
bool updmax(T& a, T b) {
  if(b > a) {
    a = b;
    return true;
  }
  return false;
}
typedef int64_t ll;

int merge(int x, int gap) {
  int r = 0;
  assert(x);
  while(gap) {
    r++;
    gap = max(0, gap - x);
    x *= 2;
  }
  return r;
}
int fast(int lhsgap, int curr, int rhsgap) {
  if(curr == 0) return 1e8;
  if(lhsgap == 0) return merge(curr, rhsgap);
  if(rhsgap == 0) return merge(curr, lhsgap);
  if(lhsgap <= curr) return 1 + merge(lhsgap + curr, rhsgap);
  if(rhsgap <= curr) return 1 + merge(rhsgap + curr, lhsgap);
  int ret = 1e9;
  for(int q = 0; q < 2; q++) {
    int need = (lhsgap + curr - 1) / curr;
    int clhs = lhsgap;
    int crhs = rhsgap;
    int ccurr = curr;
    int amt = 1;
    int cand = 0;
    while(clhs || crhs) {
      cand++;
      if(amt & need) {
        int take = min(clhs, ccurr);
        clhs -= take;
        ccurr += take;
      }
      else if(crhs) {
        int take = min(crhs, ccurr);
        crhs -= take;
        ccurr += take;
      }
      else {
        int take = min(clhs, ccurr);
        clhs -= take;
        ccurr += take;
      }
      amt *= 2;
    }
    updmin(ret, cand);
    swap(lhsgap, rhsgap);
  }
  return ret;
}
void solve() {
  int r, c;
  cin >> r >> c;
  vector<string> g(r);
  for(int i = 0; i < r; i++) cin >> g[i];
  int ret = 1e9;
  for(int q = 0; q < 2; q++) {
    vector<int> heights(c);
    for(int i = 0; i < r; i++) {
      for(int j = 0; j < c; j++) {
        if(g[i][j] == '0') heights[j] = 0;
        else heights[j]++;
      }
      vector<array<int, 2>> st;
      for(int j = 0; j < c; j++) {
        int clhs = j;
        while(sz(st) && st.back()[0] > heights[j]) {
          array<int, 2> curr = st.back(); st.pop_back();
          int lhs = curr[1];
          updmin(ret, fast(lhs, j - lhs, c - j) + fast(i+1-curr[0], curr[0], r - i - 1));
          clhs = lhs;
        }
        st.pb({heights[j], clhs});
      }
      while(sz(st)) {
        array<int, 2> curr = st.back(); st.pop_back();
        int lhs = curr[1];
        updmin(ret, fast(lhs, c - lhs, 0) + fast(i+1-curr[0], curr[0], r - i - 1));
      }
    }
    vector<string> ng(c);
    for(int i = 0; i < r; i++) for(int j = 0; j < c; j++) ng[j] += g[i][j];
    g.swap(ng);
    swap(r, c);
  }
  cout << ret << "\n";
}
// what would chika do
// are there edge cases (N=1?)
// are array sizes proper (scaled by proper constant, for example 2* for koosaga tree)
// integer overflow?
// DS reset properly between test cases
// are you doing geometry in floating points
// are you not using modint when you should

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  solve();
}