// yukicoder: No.365 ジェンガソート
// 2019.5.13 bal4u

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

#if 1
#define gc() getchar_unlocked()
#else
#define gc() getchar()
#endif
int in()
{
	int n = 0, c = gc();
	do n = 10*n + (c & 0xf), c = gc(); while (c >= '0');
	return n;
}

int f[100005];

int main()
{
	int i, N;

	N = in(); for (i = 1; i <= N; i++) f[in()] = i;
	f[0] = N+1, i = N-1;
	while (1) {
		if (f[i] > f[i+1]) break;
		i--;
	}
	printf("%d\n", i);
	return 0;
}