1095A - Repeating Cipher - CodeForces Solution

k=int(input(''))
s=input('')
c=[]
m=int(((1+8*k)**0.5-1)/2)
for n in range(1,m+1):
    if n==1:
        k=s[0]
        c.append(k)
            else:
        l=int(n*(n-1)*0.5)
        u=int(n*(n+1)*0.5)
        k=s[l:u]
        c.append(k[0])
        print(''.join(c))