#include <iostream>
#include <vector>
#include <string>
#include <iomanip>
#include <queue>
#include <cmath>
#include <algorithm>
#include <tuple>
#include <iomanip>
#include <stdio.h>
#include <numeric>
#include <map>
#include <bitset>
#include <set>
#include <stack>
#include <queue>
#include <unordered_set>


#define int long long
#define ll long long
#define ull unsigned long long
#define all(a) a.begin(), a.end()
#define pii pair<int, int>
#define pb push_back
#define ld long double


using namespace std;

const int INF = 1e17;
//const int mod = 2600000069;
//const int p = 179;

struct q {
    int x, type, id;
    q() {
        x = 0;
        type = -1;
        id = -1;
    }
    q(int x_, int type_, int id_) {
        x = x_;
        type = type_;
        id = id_;
    }
};

bool comp(q a, q b) {
    return (a.x < b.x || a.type < b.type);
}

signed main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    string s;
    cin >> s;
    int n = s.size();
    int ind1 = 0, ind2 = n - 1, loss = 0, ans = -1;
    while(ind1 < ind2) {
        if (s[ind1] == s[ind2]) {
            ind1++;
            ind2--;
        } else {
            if (s[ind1 + 1] == s[ind2]) {
                ans = ind1 + 1;
                ind1+=2;
                ind2--;
            } else if (s[ind2 - 1] == s[ind1]) {
                ans = ind2 + 1;
                ind2 -= 2;
                ind1++;
            } else {
                cout << "0";
                return 0;
            }
            loss++;
        }
    }
    if (loss > 1) {
        cout << 0;
        return 0;
    }
    cout << ans;
}
/*

*/