#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
 
#define mod 1000000007
#define pb push_back
#define mp make_pair
#define PI 3.1415926535
#define pf push_front
#define ll long long int
#define ull unsigned long long int 
typedef pair<int,int>  pii; 
uint64_t seed = reinterpret_cast<uint64_t>(new char);
mt19937_64 rd(seed);
//uniform_int_distribution<int> rg(1, n);
//int RandomNumber = rg(rd);
// vector < int > v(N,-1);   sqrtl for square root of ll
// vector of size N with initial value -1 
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> pbds;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> OST;
#define gc getchar_unlocked
 
const int N=60005;
const int M=1000005;
int upd[2005];
vector <pii> v[1005];
int main ()     
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int i,j,k,l,n,m,p;
    cin>>n>>m>>k;
    int arr[n+5][m+5];
    for(i=0;i<n;i++)
    {
        for(j=0;j<m;j++)
        {
            cin>>arr[i][j];
        }
    }
    int cnt=0;
    for(i=0;i<n;i++)
    {
        for(auto pk : v[i]){
            upd[pk.first]--;  upd[pk.second]++;
        }
        int pre=0;
        for(j=0;j<m;j++)
        {
            pre=pre+upd[j];
            int xd=pre;
            if(arr[i][j]==0){
                if(xd%2==0){
                    if((j+k-1)>=m || (i+k-1)>=n){
                        cout<<-1<<endl;  return 0;
                    }
                    upd[j]++; pre++;  upd[j+k]--;
                    v[i+k].pb({j,j+k}); 
                    cnt++;
                }  
            }
            if(arr[i][j]==1){
                if(xd%2){
                    if((j+k-1)>=m || (i+k-1)>=n){
                        cout<<-1<<endl;  return 0;
                    }
                    upd[j]++;  pre++;  upd[j+k]--;
                    cnt++;   v[i+k].pb({j,j+k}); 
                }
            }
        }
    }
    cout<<cnt<<endl;
    return 0; 
}