#include <stdio.h>
#include <stdlib.h>

#define ARRAY_NUM 100000

int main(void) {
	int i, n, max,max1, max_num, count;
	int list[ARRAY_NUM] = { };

	max = max_num = count = 0;

	scanf("%d", &n);
	for (i = 0; i < n; i++) {
		scanf("%d", &list[i]);
	}

	for (i = 0; i < n; i++) {
		if (max < list[i]) {
			max1 = max = list[i];
			max_num = i;
		}
	}


	max--;
	while (max_num-- > 0) {
		if (max == list[max_num]) {
			count++;
			max--;
		}
	}
	count++;  // include maxself

//	printf("%d", count);

	printf("%d", max1 - count);

	return 0;
}