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))1702E - Split Into Two Sets | 1703B - ICPC Balloons |
1702F - Equate Multisets | 1700A - Optimal Path |
665C - Simple Strings | 1708A - Difference Operations |
1703E - Mirror Grid | 1042A - Benches |
1676B - Equal Candies | 1705B - Mark the Dust Sweeper |
1711A - Perfect Permutation | 1701B - Permutation |
1692A - Marathon | 1066A - Vova and Train |
169B - Replacing Digits | 171D - Broken checker |
380C - Sereja and Brackets | 1281B - Azamon Web Services |
1702A - Round Down the Price | 1681C - Double Sort |
12A - Super Agent | 1709A - Three Doors |
1680C - Binary String | 1684B - Z mod X = C |
1003A - Polycarp's Pockets | 1691B - Shoe Shuffling |
1706A - Another String Minimization Problem | 1695B - Circle Game |
1702B - Polycarp Writes a String from Memory | 1701A - Grass Field |