Buggy python submission (verdict: Runtime Error):
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for i in range(l-1,-1,-1):
        for x,y in alpha2.items():
            memo[i][y]=memo[i+1][y]
        memo[i][alpha2[s[i]]]=i+1

    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Buggy python submission (verdict: Runtime Error):
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for i in range(l-1,-1,-1):
        for x,y in alpha2.items():  
            memo[i][y]=memo[i+1][y]
        memo[i][alpha2[s[i]]]=i+1
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Buggy python submission (verdict: Runtime Error):
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for i in range(l-1,-1,-1):
        for x,y in alpha2.items():  
            memo[i][y]=memo[i+1][y]
            memo[i][alpha2[s[i]]]=i+1
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Buggy python submission (verdict: Runtime Error):
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for i in range(l-1,-1,-1):
        for x,y in alpha2.items():  
            memo[i][y]=memo[i+1][y]
        memo[i][alpha2[s[i]]]=i+1
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Buggy python submission (verdict: Runtime Error):
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for i in range(l-1,-1,-1):
        for x,y in alpha2.items():  
            memo[i][y]=memo[i+1][y]
        memo[i][alpha2[s[i]]]=i+1
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Buggy python submission (verdict: Runtime Error):
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for i in range(l-1,-1,-1):
        for x,y in alpha2.items():  
            memo[i][y]=memo[i+1][y]
        memo[i][alpha2[s[i]]]=i+1
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    #s=alpha*8000
    #s="a"*200000
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    def search(n,seq):
        temp=-1
        for i in range(26):
            if memo[n][i]>temp:
                temp=memo[n][i]
        return temp,seq+1
    n,seq=0,0
    while n<=l:
        n,seq=search(n,seq)
    ans_len=seq
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n,seq=memo[temp][j],i+1
            while n<=l:
                n,seq=search(n,seq)
            if seq==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Buggy python submission (verdict: Runtime Error):
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    def search(n,seq):
        temp=-1
        for i in range(26):
            if memo[n][i]>temp:
                temp=memo[n][i]
        return temp,seq+1
    n,seq=0,0
    while n<=l:
        n,seq=search(n,seq)
    ans_len=seq
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n,seq=memo[temp][j],i+1
            while n<=l:
                n,seq=search(n,seq)
            if seq==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input=sys.stdin.readline
    sys.setrecursionlimit(100000)
    s=input()
    l=len(s)
    alpha="abcdefghijklmnopqrstuvwxyz"
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    def search(n,seq):
        if n==l+1:
            return seq
        temp=-1
        for i in range(26):
            if memo[n][i]>temp:
                temp=memo[n][i]
        return search(temp,seq+1)
    ans_len=search(0,0)
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            ls=search(memo[temp][j],i+1)
            if ls==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input=sys.stdin.readline
    sys.setrecursionlimit(100000)
    s=input()
    l=len(s)
    alpha="abcdefghijklmnopqrstuvwxyz"
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    def search(n,seq):
        if n==l+1:
            return seq
        temp=-1
        for i in range(26):
            if memo[n][i]>temp:
                temp=memo[n][i]
        return search(temp,seq+1)
    ans_len=search(0,0)
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            ls=search(memo[temp][j],i+1)
            if ls==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Buggy python submission (verdict: Runtime Error):
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    l=len(s)
    alpha="abcdefghijklmnopqrstuvwxyz"
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    def search(n,seq):
        if n==l+1:
            return seq
        temp=-1
        for i in range(26):
            if memo[n][i]>temp:
                temp=memo[n][i]
        return search(temp,seq+1)
    ans_len=search(0,0)
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            ls=search(memo[temp][j],i+1)
            if ls==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
def main():
    import sys
    input=sys.stdin.readline
    s=input()
    alpha="abcdefghijklmnopqrstuvwxyz"
    l=len(s)
    alpha2={j:i for i,j in enumerate(alpha)}
    memo=[[0]*26 for _ in range(l,-1,-1)]
    for i in range(26):
        memo[l][i]=l+1
    for x,y in alpha2.items():
        for i in range(l-1,-1,-1):
            if s[i]==x:
                memo[i][y]=i+1
            else:
                memo[i][y]=memo[i+1][y]
    
    search=[1]*(l+2)
    search[l+1]=0
    for i in range(l-1,-1,-1):
        m=max([memo[i][j] for j in range(26)])
        if m!=l+1:
            search[i]=search[m]+1
    
    n,seq=0,0
    ans_len=search[0]
    ans=""
    temp=0
    for i in range(ans_len):
        for j in range(26):
            n=memo[temp][j]
            seq=search[n]+i
            if seq+1==ans_len:
                ans+=alpha[j]
                temp=memo[temp][j]
                break
    print(ans)
if __name__=='__main__':
    main()