793A - Oleg and shares

#include<iostream>
#include<vector>
#include<string>
#include<set>
#include<map>
#include<algorithm>
#include<queue>
#include<list>
#include<stack>
#include<cstdio>
#include<fstream>
#include<numeric>
#include<functional>
#include<utility>
#include<memory>
using namespace std;
using namespace placeholders;

typedef long long int ll;

int main(){
	ll n, k;
	while (cin >> n >> k){
		vector<ll> price;
		ll min_p = INT_MAX;
		for (ll i = 0; i < n; i++){
			ll temp;
			cin >> temp;
			price.push_back(temp);
			if (temp < min_p) min_p = temp;
		}
		ll res = 0;
		for (int i = 0; i < n; i++){
			if ((price[i] - min_p) % k){
				res = -1;
				break;
			}
			else{
				res += ((price[i] - min_p) / k);
			}
		}
		cout << res << endl;
	}
	//	system("pause");
	return 0;
}