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#include <bits/stdc++.h>
using namespace std;
//{
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define VAR(v, i) __typeof(i) v=(i)
#define all(v) (v).begin(),(v).end()
#define FORE(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)


#define PII pair<int,int>
#define st first
#define nd second
#define pb push_back
#define lint long long int
#define VI vector<int>

#define sim template < class c
#define ris return * this
#define dor > debug & operator <<
#define eni(x) sim > typename \
  enable_if<sizeof dud<c>(0) x 1, debug&>::type operator<<(c i) {
sim > struct rge { c b, e; };
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c* x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
~debug() { cerr << endl; }
eni(!=) cerr << boolalpha << i; ris; }
eni(==) ris << range(begin(i), end(i)); }
sim, class b dor(pair < b, c > d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
	*this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
};
//{
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "

#define make( x) int (x); scanf("%d",&(x));
#define make2( x, y) int (x), (y); scanf("%d%d",&(x),&(y));
#define make3(x, y, z) int (x), (y), (z); scanf("%d%d%d",&(x),&(y),&(z));
#define make4(x, y, z, t) int (x), (y), (z), (t); scanf("%d%d%d%d",&(x),&(y),&(z),&(t));
#define makev(v,n) VI (v); FOR(i,0,(n)) { make(a); (v).pb(a);} 
#define IOS ios_base::sync_with_stdio(0)
#define HEAP priority_queue

#define read( x) scanf("%d",&(x));
#define read2( x, y) scanf("%d%d",&(x),&(y));
#define read3(x, y, z) scanf("%d%d%d",&(x),&(y),&(z));
#define read4(x, y, z, t) scanf("%d%d%d%d",&(x),&(y),&(z),&(t));
#define readv(v,n) FOR(i,0,(n)) { make(a); (v).pb(a);}
#define jeb() fflush(stdout);
//}

#define PDD pair<double, double>

int n;
char s[1234567];
char C = 'c';

int main() {
	scanf("%s", s);
	n = strlen(s);
	
	for (char x = 'a'; x < 'c'; x++) {
		int cnt = 0;
		FOR(i,0,n) if (s[i] == x) cnt++;
		if (cnt % 2 == 0) C = x;
	}
	if (C == 'c') {
		printf("-1\n");
		return 0;
	}
	
	int cnt = 0;
	FOR(i,0,n) if (s[i] == C) cnt++;
	int k = cnt/2;
	
	int cntL = 0;
	FOR(i,0,n/2) if (s[i] == C) cntL++;
	 
	if (cntL < k) {
		FOR(i,0,n/2) swap(s[i], s[n-1-i]);
	}

		cntL = 0;
	FOR(i,0,n/2) if (s[i] == C) cntL++;


	lint ans = 0;
	int lft = cntL;
	int pos = (n+1)/2;
	FORD(i,n/2-1,0) {
		if (s[i] == C) {
			if (lft > k) {
				while (s[pos] == C) pos++;
				ans += pos - i;
				swap(s[pos], s[i]);
				lft--;
			}
		}
	}
	VI p1, p2;
	FORD(i,n/2-1,0) if (s[i] == C) p1.pb(i);
	FOR(i,n/2,n) if (s[i] == C) p2.pb(i);
	
	FOR(i,0,k) {
		ans += abs(p1[i]-(n-1-p2[i]));
	}
	printf("%lld\n", ans);
}