/******************************************************************************

                              Online C++ Compiler.
               Code, Compile, Run and Debug C++ program online.
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*******************************************************************************/

#include <iostream>

using namespace std;

int main()
{
    int n, k, m, x = 1000, w = 1, t = 0, max = 0 , l;
    cin>>n;
    cin>>k;
    int a[1000];
    int b[1000];
    int c[1000];
    for(int i = 0; i < n; i++)
    {
        a[i] = 0;
        b[i] = 0;
    }
    for(int i = 0;i < n; i++)
    {
        cin>>m;
        if(a[m-1] == 0)
        {
            c[t] = m-1;
            t++;
        }
        a[m-1]++;

    }
    for(int i = 0; i < t; i++)
    {
        if(max < a[с[i]]
        {
            max = a[c[i]];
        }
    }
    for(int i = 0; i < t; i++)
    {
        if(a[c[i]] == max)
        {
            l++;
        }
    }
    if( (max > (n/k) + 1) or ( (max == (n/k) + 1) and (l > n%k) ) )
    {
        cout<<-1;
    }
    else
    {
        for(int i = 0; i < t; i++)
        {
            if(max == (n/k) + 1 and a[c[i]] == max)
            {
                for(int j = 0; j < a[c[i]]; j++)
                {
                    b[w] = c[i];
                    w += k
                }
            }

        }
    }

}