#include <bits/stdc++.h>   using namespace std;   signed main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     cout.tie(NULL);     long long int n, m, k, count = 0;     cin >> n >> m >> k;     long long int s = n * m;     long long int a[s], b[s];     for (long long int i = 0; i < s; i++) cin >> a[i];     sort(a, a + s);     for (long long int i = 0; i < s; i++) {       b[i] = abs(a[i] - a[s / 2]);       if (b[i] % k != 0) {         cout << -1;         return 0;       } else {         count += b[i] / k;       }     }     cout << count;   }   