3
-1 1 -1
 4
45 -1 41 -1
 1
-1
 5
40 -1 44 46 48
 6
43 40 37 34 -1 -1
 7
-1 2 4 -1 4 1 5
 19
23 26 -1 -1 35 38 41 -1 -1 -1 53 -1 59 62 6 7 8 9 -1
 6
-1 2 6 -1 -1 6
 16
3 8 13 18 23 -1 -1 -1 43 48 53 45 -1 -1 -1 -1
 13
25 24 23 22 24 27 -1 33 -1 2 2 2 -1
 12
-1 17 -1 54 -1 64 -1 74 79 84 -1 94
 8
-1 12 14 16 18 20 -1 -1
 13
2 -1 3 1 3 1 -1 1 3 -1 -1 1 1
 5
-1 40 42 -1 46
 2
1000000000 -1
 14
-1 5 3 -1 -1 31 31 31 -1 31 -1 -1 4 7
 3
-1 1000000000 999999999
 7
32 33 34 -1 -1 37 38
 1
1000000000
 10
29 27 -1 23 42 -1 -1 45 -1 -1
 3
39 42 -1
 15
-1 28 -1 32 34 26 -1 26 -1 -1 26 26 26 -1 -1
 3
1000000000 999999999 1000000000
 17
-1 -1 -1 -1 64 68 72 -1 45 46 47 48 49 50 51 52 53
 3
-1 1 1000000000
 2
-1 1000000000
 3
999999999 -1 1000000000
 1
1
 2
1000000000 1000000000
 3
999999999 1000000000 -1
 7
11 8 5 -1 -1 -1 -1
 3
-1 1 2
 2
-1 21
 8
-1 -1 1 7 -1 9 5 2
 11
9 21 17 13 -1 -1 -1 -1 -1 -1 -1
 3
-1 1000000000 -1
 6
-1 6 1 -1 -1 -1
 1
65
 20
-1 32 37 -1 -1 -1 57 -1 -1 40 31 33 -1 -1 39 47 43 -1 35 32
 5
-1 1 7 -1 5
 18
21 19 -1 -1 -1 48 50 -1 54 -1 5 1 -1 -1 -1 37 36 35
 9
42 39 36 33 -1 -1 -1 34 39
 2
-1 -1

1
 1
 1
 1
 1
 3
 2
 2
 2
 3
 2
 1
 6
 1
 1
 3
 1
 1
 1
 2
 1
 2
 2
 2
 2
 1
 2
 1
 1
 1
 2
 2
 1
 3
 3
 1
 2
 1
 5
 2
 4
 2
 1

import sys,math

def solve(cleared,n):
	if len(cleared) < 2:
		return 1
	ans = 1
	initial_rate = float(cleared[1][1] - cleared[0][1]) / (cleared[1][0] - cleared[0][0])
	# check for unboundness (left)
	if cleared[0][0] != 0:
		ghost_number = cleared[0][1] - initial_rate
		if  ghost_number < 1: # ghost_number > 1e9 or
			ans += 1
	for i in range(1,len(cleared)):
		numerator, denominator = cleared[i][1] - cleared[i-1][1],(cleared[i][0] - cleared[i-1][0])
		new_rate = float(numerator) / denominator
		# in case there are more -1 that would make the rate not integer
		if abs(numerator) < denominator and numerator != 0:
			ans += 1
		if new_rate != initial_rate:
			ans += 1
			if i < len(cleared) - 1:
				initial_rate = float(cleared[i+1][1] - cleared[i][1]) / (cleared[i+1][0] - cleared[i][0])
	if cleared[-1][0] != n - 1:
		ghost_number = cleared[-1][1] + initial_rate
		if ghost_number < 1: # ghost_number > 1e9 or 
			ans += 1
	return ans
			

if __name__ == '__main__':
	n = int(raw_input())
	if n == 1:
		raw_input()
		print 1
	else:
		ans,cross,input = 0,[0],map(int,raw_input().split())
		ans = solve([i for i in enumerate(input) if i[1] != -1],n)
		print ans
