#include <stdio.h>
#include <stdlib.h>
#define L 9
int v[801],n;
int bin(int x, int y){
    int pas, z;
    z=y+1;
    pas = z + 1<<L;
    while( pas != 0 ){
        if(pas<=n)
            if( v[x]+v[y] < v[z+pas] ){
                z=z+pas;
            }
        pas=pas/2;
    }
    if(v[x] + v[y] >= v[z+pas])
        return z+pas;
    else
        return z;
}
int main()
{
    FILE *f1 = fopen ("nrtri.in","r"), *f2 = fopen ("nrtri.out","w");
    int i,j,tri=0;
    fscanf(f1,"%d",&n);
    for(i=1;i<=n;i++)
        fscanf(f1,"%d",&v[i]);
    int aux;
    for(i=1;i<n;i++)
        if(v[i]>v[i+1]){
            aux = v[i];
            v[i]= v[i+1];
            v[i+1] = aux;
        }
    for(i=1;i<=n-2;i++)
        for(j=i+1;j<=n-1;j++)
            if(bin(i,j)!=j+1)
                tri=tri+bin(i,j)-j;
    fprintf(f2,"%d",tri);
    return 0;
}