#include <bits/stdc++.h>

#define INF (1 << 30)
#define LLINF (1LL << 62)
#define mod 666013

using namespace std;

int n, i, sol;
int v[100005], l[100005], rat[100005];

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

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

    rat[n] = INF;
    l[n] = 1;
    for(i = n - 1; i >= 1; i--)
    {
        rat[i] = v[i + 1] - v[i];

        if(rat[i] == rat[i + 1])
            l[i] = 1 + l[i + 1];
        else
            l[i] = 2;
    }

    for(i = 1; i <= n; i++)
        sol += l[i] / 2;
    printf("%d", sol);

    return 0;
}