#include<stdio.h>
#define ll long long
#define dec 200003

ll sol;
int d[400009][2],n,ant,v;

int main ()
{
    int i;
    freopen("numarare.in","r",stdin);
    freopen("numarare.out","w",stdout);
    scanf("%d",&n);
    scanf("%d",&ant);
    for(i=1;i<n;i++)
    {
        scanf("%d",&v);
        d[ant-v+dec][i&1]++;
        sol+=d[ant-v+dec][i&1];
        ant=v;
    }
    printf("%lld\n",sol);
    return 0;
}