Brigada

n, b, c = map(int, input().split())
heights = []
for i in range(n):
    heights.append(int(input()))
heights.sort()

l = -1
r = heights[-1]

def check(g, b, c, heights):
    i = 0
    while b:
        if i + c - 1 >= len(heights):
            return False
        if heights[i+c-1] - heights[i] <= g:
            b -= 1
            i = i + c
        else:
            i += 1
    return True

while r - l > 1:
    g = l + (r - l) // 2
    if check(g, b, c, heights):
        r = g
    else:
        l = g

print(r)