#include <stdio.h>

long n, i, varf, last_thingy, rez, x[1000010];

int main()
{
	freopen ("operatii.in", "rt", stdin);
	freopen ("operatii.out", "wt", stdout);

	scanf("%ld", &n);

	for (i = 1; i <= n; i ++)
		scanf("%ld", &x[i]);

	last_thingy = 0;
	varf = 0;
	for (i = 1; i <= n; i ++)
	{
		if (x[i] > x[i + 1] && !varf)
			varf = x[i];
		else
		if (x[i] < x[i + 1] && varf)
		{
			rez += varf - last_thingy;
			last_thingy = x[i];
			varf = 0;
		}
	}

	if (varf)
		rez += varf - last_thingy;
	printf("%ld\n", rez);
	return 0;
}