Little penguin Polo has an *n* × *m* matrix, consisting of integers. Let's index the matrix rows from 1 to *n* from top to bottom and let's index the columns from 1 to *m* from left to right. Let's represent the matrix element on the intersection of row *i* and column *j* as *a*<sub class="lower-index">*ij*</sub>.

In one move the penguin can add or subtract number *d* from some matrix element. Find the minimum number of moves needed to make all matrix elements equal. If the described plan is impossible to carry out, say so.
The first line contains three integers *n*, *m* and *d* (1 ≤ *n*, *m* ≤ 100, 1 ≤ *d* ≤ 10<sup class="upper-index">4</sup>) — the matrix sizes and the *d* parameter. Next *n* lines contain the matrix: the *j*-th integer in the *i*-th row is the matrix element *a*<sub class="lower-index">*ij*</sub> (1 ≤ *a*<sub class="lower-index">*ij*</sub> ≤ 10<sup class="upper-index">4</sup>).
# https://codeforces.com/problemset/problem/289/B

"""
There is an nxm matrix with integer entries.
In a move the penguin can add or subtract a number d from some matrix element
Find the min number of moves needed to make all entries equal.

First the structure of a matrix is in not important
What is important is that all entries are the same modulo d

We can add or subtract d. We can argue that the value that
will yield the least number of moves must exist within the range
of the current values
"""


def main():
    n, m, d = map(int, input().split())

    entries = []
    for i in range(n):
        entries.extend(list(map(int, input().split())))

    residues = [entry % d for entry in entries]
    if residues.count(residues[0]) != len(residues):
        return -1

    candidates = list(range(min(entries), max(entries)+1, d))
    min_moves = sum([abs(entry - candidates[0]) // d for entry in entries])  # Clearly an upper bound
    for candidate in candidates:
        moves = sum([abs(entry - candidate) // d for entry in entries])

        if moves < min_moves:
            min_moves = moves

    return min_moves


if __name__ == '__main__':
    print(main())

