c575

/* c575             */
/* AC (11ms, 636KB) */
#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

typedef long long int64;

vector<int64> point;

bool solve(int r, int N, int K)
{
    int cnt = 0, Range;
    for(auto it = point.begin(); it != point.end();)
    {
        Range = *it + r;
        ++cnt;
        if(cnt > K)
            return false;
        if(Range >= point[N - 1] && cnt <= K)
            return true;
        while(Range >= *it)
            ++it;
    }
    return false;
}
int main()
{
    for(int N, K, result; ~scanf("%d %d", &N, &K) && N && K;)
    {
        point.resize(N);
        for(int i = 0; i < N && scanf("%lld", &point[i++]););
        sort(point.begin(), point.end());

        int R = point[N - 1] - point[0], L = 1;
        if(K == 1)
        {
            printf("%d\n", R);
            continue;
        }
        else
            while(L < R)
            {
                int M = (R + L) >> 1;
                if(solve(M, N, K))
                    R = M;
                else
                    L = M + 1;
            }
        printf("%d\n", R);
    }
    return 0;
}