#include <cstdio>
#define INF 0x7ffffff
int n, s = INF, d[30010], f[30010][4];
int main() {
	freopen("egroup.in", "r", stdin);
	freopen("egroup.out", "w", stdout);
	scanf("%d\n", &n);
	for(int i=1; i<=n; i++)
		scanf("%d", d+i);
	for(int j=1; j<=3; j++) {
		for(int i=1; i<=n; i++) {
			f[i][j] = INF;
			for(int k=1; k<=j; k++)
				if(f[i][j] > f[i-1][k])
					f[i][j] = f[i-1][k];
			if(d[i] != j)
				f[i][j]++;
		}
		if(s > f[n][j])
			s = f[n][j];
	}
	for(int j=3; j>=1; j--) {
		for(int i=1; i<=n; i++) {
			f[i][j] = INF;
			for(int k=j; k<=3; k++)
				if(f[i][j] > f[i-1][k])
					f[i][j] = f[i-1][k];
			if(d[i] != j)
				f[i][j]++;
		}
		if(s > f[n][j])
			s = f[n][j];
	}
	printf("%d\n", s);
	return 0;
}