#include <stdio.h>
#include <ctype.h>

int main(int argc, char *argv[]) {

	#define CASE_BIT ('A' ^ 'a')
	#define MAX_LENGTH 65536
	static char stack[MAX_LENGTH];
	FILE *input;
	int c, top;
       
	if (input = fopen("input.txt", "r")) {
		top = -1;
		while (isalpha(c = fgetc(input))) {
			if (top >= 0 && (c ^ CASE_BIT) == stack[top]) {
				--top;
			}
			else {
				if (++top < MAX_LENGTH) stack[top] = c;
				else return 1;
			}
		}
		fclose(input);
	}
	else return 2;

	printf("%d\n", top + 1);
	return 0;
}