import sys
INF = float('inf')
#10**20,2**63,float('inf')
MOD = 10**9 + 7
MOD2 = 998244353
#from collections import defaultdict
def solve():
    def II(): return int(sys.stdin.readline())
    def LI(): return list(map(int, sys.stdin.readline().split()))
    def LC(): return list(input())
    def IC(): return [int(c) for c in input()]
    def MI(): return map(int, sys.stdin.readline().split())
    S = LC()
    Num = 1
    for i,s in enumerate(S):
        if s == "a":
            Num = i+2
        else:
            break
    print("a"*Num)
    return
solve()
#sys.setrecursionlimit(10 ** 6)#再帰関数ではコメントにしないこと！！