n = int(input())
s = input()
m = [[0 for j in range(26)] for i in range(26)]
A = ord('A')
for i in range(n - 1):
m[ord(s[i]) - A][ord(s[i + 1]) - A] += 1
x, y = 0, 0
for i in range(26):
for j in range(26):
if m[i][j] > m[x][y]:
x, y = i, j
print(chr(A + x)+ chr(A + y))
1312. Minimum Insertion Steps to Make a String Palindrome | 1092. Shortest Common Supersequence |
1044. Longest Duplicate Substring | 1032. Stream of Characters |
987. Vertical Order Traversal of a Binary Tree | 952. Largest Component Size by Common Factor |
212. Word Search II | 174. Dungeon Game |
127. Word Ladder | 123. Best Time to Buy and Sell Stock III |
85. Maximal Rectangle | 84. Largest Rectangle in Histogram |
60. Permutation Sequence | 42. Trapping Rain Water |
32. Longest Valid Parentheses | Cutting a material |
Bubble Sort | Number of triangles |
AND path in a binary tree | Factorial equations |
Removal of vertices | Happy segments |
Cyclic shifts | Zoos |
Build a graph | Almost correct bracket sequence |
Count of integers | Differences of the permutations |
Doctor's Secret | Back to School |