#include <stdio.h>
#define maxN 	2010

int C[maxN][maxN], V[maxN];

int main () {
	int Sol = 0, i, j, N;

	freopen("numarare.in", "r", stdin);
	freopen("numarare.out", "w", stdout);

	scanf("%d", &N);

	for (i = 1; i <= N; ++ i)
		scanf("%d", &V[i]);

	for (i = N; i; -- i) {
		C[i][i + 1] = 1;
		for (j = i + 3; j <= N; j += 2)
			C[i][j] = C[i + 1][j - 1] && V[i] + V[j] == V[i + 1] + V[j - 1];
	}

	for (i = 1; i <= N; ++ i)
		for (j = i + 1; j <= N; j += 2)
			Sol += C[i][j];

	printf("%d\n", Sol);
	return 0;
}