// 長い夜の終わりを信じながら
// Think twice, code once.
#include <cstdio>
#include <string>
#include <cstring>
#include <iostream>
#include <algorithm>
#define eputchar(c) putc(c, stderr)
#define eprintf(...) fprintf(stderr, __VA_ARGS__)
#define eputs(str) fputs(str, stderr), putc('\n', stderr)
using namespace std;

int fib[35], ans = 0x3f3f3f3f, mx[3000005], id[3000005];
int n, dp[150005][35];
string s;

int main() {
	fib[0] = fib[1] = 1;
	for (int i = 2; i <= 32; i++) fib[i] = fib[i - 1] + fib[i - 2];
	mx[3] = 2;
	id[1] = 1, id[2] = 0, id[3] = 1;
	for (int i = 4; i <= 3000000; i++) {
		mx[i] = mx[i - 1] + (fib[mx[i - 1] + 1] < i);
		id[i] = id[i - fib[mx[i]]];
	}
	// eprintf("%d\n", fib[31]);
	cin >> s;
	n = s.length();
	s = " " + s;
	for (int i = 1; i <= n; i++)
		if (s[i] == 'b') dp[i][0] = 1, dp[i][1] = 0;
		else dp[i][0] = 0, dp[i][1] = 1;
	for (int j = 2; j <= 30; j++)
		for (int i = 1; i <= n; i++) dp[i][j] = dp[i][j - 1] + dp[i + dp[i][j - 1]][j - 2];
	for (int i = 1; i <= 15 * n; i++)
		if ((id[i] >= 1 ? 'a' : 'b') == s[1]) {
			// eprintf("%d\n", i);
			int now = i, p = 1;
			while (p <= n) {
				int id = ::id[now];
				while (id > 1 && p + dp[p][id] == n + 1) id--;
				// eprintf("%d %d %d\n", now, id, p);
				p += dp[p][id];
				now += fib[id];
			}
			ans = min(ans, now - i);
		}
	printf("%d\n", ans);
	return 0;
}