N,K=map(int, input().split())
S=input()
ans=[]
t=0
for i in range(N-K+1):
    ans.append(S[i+K-1])
    t+=1
for i in range(K-1):
    j = K-2-i if t&1 else i
    ans.append(S[j])
print(''.join(ans))