#include <bits/stdc++.h>
using namespace std;

const int N = 5e6 + 50;
const int M = 1e9 + 7;

int p[N], pi[N];
int h[N], hr[N];
int n;

int sum(int a, int b) {return (a + b) % M;}
int mult(long long a, long long b) {return (a * b) % M;}

int get(int l, int r) {
    return mult(pi[l], sum(h[r], M - (l - 1 >= 0 ? h[l - 1] : 0)));
}
int getr(int l, int r) {
    return mult(pi[n - r - 1], sum(hr[l], M - (r + 1 < n ? hr[r + 1] : 0)));
}

int bp(int x, int y) {
    if (!y) {
        return 1;
    }
    if (y & 1) {
        return mult(x, bp(x, y - 1));
    }
    int a = bp(x, y >> 1);
    return mult(a, a);
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int nm[360]{0};
    nm['A'] = 0;
    nm['C'] = 1;
    nm['G'] = 2;
    nm['T'] = 3;

    string s;
    cin >> s;
    n = (int)s.size();
    p[0] = 1;
    pi[0] = 1;
    for (int i = 1; i < N; i++) {
        p[i] = mult(p[i - 1], 5);
        pi[i] = bp(p[i], M - 2);
    }

    for (int i = 0; i < n; i++) {
        if (i) {
            h[i] = h[i - 1];
        }
        h[i] = sum(h[i], mult(p[i], nm[s[i]]));
    }

    for (int i = n - 1; i >= 0; i--) {
        if (i + 1 < n) {
            hr[i] = hr[i + 1];
        }
        hr[i] = sum(hr[i], mult(p[n - i - 1], nm[s[i]]));
    }

    int l = 0;
    int r = n - 1;
    int L = 0, R = n - 1;
    int it = 0;
    while (l < n) {
        if (it & 1) {
            int len = R - r + 1;
            if (r - len >= L && r <= R) {
                if (get(r, R) == getr(r - len, r - 1)) {
                    R = r - 1;
                }
            }
            r--;
        } else {
            int len = l - L + 1;
            if (l + len <= R && l >= L) {
                if (get(L, l) == getr(l + 1, l + len)) {
                    L = l + 1;
                }
            }
            l++;
        }

        it++;
    }
    cout << R - L + 1;
}