def highestValuePalindrome(s, n, k):      
    s = list(s)
    s2=s.copy()
    for i in range(int(n/2)+1):
        if s[i]!=s[n-i-1]:
            s[i]=s[n-i-1]=max(s[i], s[n-i-1])
            k-=1
        if k<0:
            return '-1'
    
    i=0
    while k>0 and i<int(n/2)+1:
        if s[i]!='9':
            if s[i]==s2[i] and s[n-i-1]==s2[n-i-1] and i!=n-i-1:
                if k>=2:
                    s[i]=s[n-i-1]='9'
                    k-=2
            else:
                s[i]=s[n-i-1]='9'
                k-=1
        i+=1
        
    return ''.join(s)