#include <stdio.h>

int main()
{
	char S[200000+1];
	scanf("%s", S);

	int l = 0;
	for (int j = 0; S[j]; j++)
		for (int i = j, a = 0; S[i]; i++) {
			if (S[i] == 'A')
				a++;
			else
				a--;
			if (a == 0 && l < i-j+1)
				l = i-j+1;
		}

	printf("%d\n", l);
	return 0;
}