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s=input()
if len(s)%2==0 and s.count("a")%2==1:
    print(-1)
else:
    t=[]
    for i in range(len(s)//2):
        if s[i]>s[-i-1]:
            t.append(1)
        elif s[i]<s[-i-1]:
            t.append(-1)
        else:
            t.append(0)
    i=0
    j=0
    r=0
    n=len(t)
    while i<n:
        #print(i)
        while i<n and t[i]==0:
            i+=1
        if i==n:
            break
        j=i+1
        tt=-t[i]
        while j<n and i<j:
            if t[j]==0:
                r+=j-i
                i+=1
            elif t[j]==tt:
                r+=2*(j-i)-1
                i+=2
            j+=1
        if j==n:
            break
    n-=i
    if len(s)%2==1:
        r+=(n*(n+1))//2
    else:
        r+=(n*n)//2
    print(r)