Codeforces Round #241 (Div. 2) D

#include <stdio.h>
#include <string.h>

const int N = 200005;
__int64 n, i, j;
__int64 a[N];

int main() {
	__int64 ans = 0;
	scanf("%I64d", &n);
	for (i = 0; i < n; i++)
		scanf("%I64d", &a[i]);
	i = 0;
	__int64 s1 = 0;
	while (i < n) {
		s1 = 0;
		while (a[i] == -1 && i < n) {
			s1++;
			i++;
		}
		__int64 s = i;
		if (i < n)
			i++;
		while (a[i] == -1 && i < n) {
			i++;
		}
		if (i == n) {
			ans++;
			break;
		}
		__int64 e = i, d;
		if ((a[e] - a[s]) % (e - s) == 0) {
			d = (a[e] - a[s]) / (e - s);
		}
		else {
			ans++;
			continue;
		}
		if (d > 0 && s1 > (a[s] - 1) / d) {
			ans++;
			i = e;
			continue;
		}
		__int64 sum = a[s];
		for (j = s + 1; j < n; j++) {
			sum += d;
			if (sum < 1) {
				i = j;
				ans++;
				break;
			}
			if (a[j] != -1 && sum != a[j]) {
				i = j;
				ans++;
				break;
			}
		}
		if (j == n) {
			i = n;
			ans++;
		}
	}
	printf("%I64d\n", ans);
	return 0;
}