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

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

	#define CASE_BIT ('A' ^ 'a')
	#define MAX_LENGTH 65536
	static char stack[MAX_LENGTH];
	FILE *input;
	int remove, c, shortest = INT_MAX, top;

	for (remove = 'a'; remove <= 'z'; ++remove) {
		if (input = fopen("input.txt", "r")) {
			top = -1;
			while (isalpha(c = fgetc(input))) {
				if ((c | CASE_BIT) != remove) {
					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;
		if (shortest > top) shortest = top;
	}

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