import heapq

def jumping_stones(stones, m):
    n = len(stones)
    distance = []
    for i in range(1, n):
        distance.append(stones[i] - stones[i - 1])

    heapq.heapify(distance)
    
    for _ in range(m):
        first = heapq.heappop(distance)
        second = heapq.heappop(distance)
        heapq.heappush(distance, first + second)
    
    return distance[0]

if __name__ == '__main__':
    stones = [0]
    nums = [int(num) for num in input().split()]
    l = nums[0]
    n = nums[1]
    m = nums[2]
    for i in range(n):
        stones.append(int(input()))
    stones.append(l)
    print(jumping_stones(stones, m))