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#include <cstdio>
#include <cassert>
#include <cstring>

using namespace std;

const int maxlen = 200002;

char t[maxlen];
int len;

int calc_result()
{
        int l, r;
        int result = 0;

        l = 0;
        r = len-1;

        while(1) {
                int l2, r2;

                while(l < r && t[l] == t[r]) {
                        ++l;
                        --r;
                }

                if (l >= r) {
                        return result;
                }

                l2 = l+1;
                r2 = r-1;

                while(l2 < r && t[l2] == t[l]) {
                        ++l2;
                }

                while(l < r2 && t[r2] == t[r]) {
                        --r2;
                }

                if (l2 >= r && l >= r2) {
                        return -1;
                }
                
                if (l2-l < r-r2) {
                        t[l2] = t[l];
                        result += l2-l;
                } else {
                        t[r2] = t[r];
                        result += r-r2;
                }
                //printf("%s\n", t);
                ++l;
                --r;
        }
}

int main()
{
        scanf("%s\n", t);
        len = strlen(t);

        printf("%d\n", calc_result());

        return 0;
}