def pr():
    p = []
    mi = 0
    for i in flag:
        l = i - mi
        mi = i
        p.append(l)
    p.append(a - mi)
    last.append(min(p))
    return

def dfs(x):
    if len(flag) == b - c:
        pr()
        return
    for i in range(x+1, b):
        flag.append(s[i])
        dfs(i)
        flag.remove(flag[len(flag) - 1])

a, b, c = map(int, input().split())
s = []
last = []
for i in range(b):
    x = int(input())
    s.append(x)
for i in range(b - c):
    flag = []
    flag.append(s[i])
    dfs(i)
print(max(last))