#include <stdio.h>

long long N, ans, i, u;

long long A[1048576];

void read()
{
	freopen("operatii.in", "r", stdin);

	for (scanf("%ld", &N), i = 1; i <= N; i++)
		scanf("%ld", A+i);

}

void write()
{
	freopen("operatii.out", "w", stdout);

	printf("%ld\n", ans);
}

void solve()
{
	for (i = 1; i <= N; u = A[i++])
		if (A[i] > u)
			ans += A[i] - u;
}

int main()
{
	read();

	solve();

	write();

	return 0;
}