CMGB

#include <bits/stdc++.h>
#define nmax 10005
using namespace std;

int N, M, st[nmax], dr[nmax], ans;
bool viz[nmax];
vector <int> L[nmax];
int n, m, a[105][105], b[105][105];

bool Cupleaza(int k)
{
    if(viz[k]) return false;
    viz[k] = true;
    for(auto i : L[k])
    {
        if(!dr[i])
        {
            st[k] = i;
            dr[i] = k;
            return true;
        }
    }
    for(auto i : L[k])
        if(Cupleaza(dr[i]))
        {
            st[k] = i;
            dr[i] = k;
            return true;
        }
    return false;
}

void Read()
{
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
        {
            cin >> a[i][j];
            if ((i + j) % 2 == 0) b[i][j] = ++N;
            else b[i][j] = ++M;
        }
}

void Graf()
{
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            if ((i + j) % 2 == 0 && a[i][j] == 1)
            {
                if (a[i-1][j] == 1) L[ b[i][j] ].push_back(b[i-1][j]);
                if (a[i+1][j] == 1) L[ b[i][j] ].push_back(b[i+1][j]);
                if (a[i][j+1] == 1) L[ b[i][j] ].push_back(b[i][j+1]);
                if (a[i][j-1] == 1) L[ b[i][j] ].push_back(b[i][j-1]);
            }
}

void Rezolva()
{
    int i, gata = 0;
    while(!gata)
    {
        gata = 1;
        for(i = 1; i <= N; i++) viz[i] = 0;
        for(i = 1; i <= N; i++)
            if(st[i] == 0 && Cupleaza(i))
            {
                ++ans;
                gata = 0;
            }
    }
    cout << ans;
}

int main()
{
    Read();
    Graf();
    Rezolva();
    return 0;
}