import math
 
 
info = [int(i) for i in input().split()]
arr = [int(i) for i in input().split()]
N, L, K = info[0], info[1], info[2]
if K > N - L:
    print(-1)
    exit(0)
table = [[0 for i in range(N)] for j in range(N)]
for i in range(1, N):
    for j in range(N - i, N):
        table[i][j] = math.inf
for i in range(N - 1):
    c = 0
    for j in range(i + 1, N):
        if arr[j] > arr[i]:
            c += 1
    table[i][0] = c
for i in range(1, N):
    for j in range(N - i):
        table[j][i] = math.inf
        c = 0
        for k in range(j + 1, N - i + 1):
            if arr[k] > arr[j]:
                # c += 1
                table[j][i] = min(table[j][i], table[k][i - 1] + c)
                c += 1
c = 0
for i in range(L - 1):
    if arr[i] >= arr[L - 1]:
        c += 1
if table[L - 1][K - 1] == math.inf:
    print(-1)
else:
    print(table[L - 1][K - 1] + c)
# for item in table:
#     print(item)
    
# print(table[0][0])
# print(table[0][-1])