def Find_It(N, X, K, S):
S=list(s)
chunks = [S[i:i + X] for i in chunks]
numbers = [sorted(set(i)) for i in chunks]
occur = [len(x) for x in numbers]
for i in range(len(occur) - 2, -1, -1):
occur[i] = occur[i] * occur[i + 1]
if k > occur[0]:
return -1
occur.append(1)
res = []
K = K -1
for i in range (1, len(occur)):
div = k // occur[i]
res.append(numbers[i - 1][div])
K = K % occur[i]
print(''.join(res))
x = input();
y = input();
z=[]
a=[]
z = x. split ('');
for i in z:
a.append(int(i))
Find_It(a[0], a[1], a[2],y)