#include<cstdio>
#include<algorithm>

using namespace std;

const int nmax=805;

int v[nmax];

int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    int n,i,j,nr,cnt=0,st,dr,med;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
        scanf("%d",&v[i]);
    sort(v+1,v+n+1);
    for(i=3;i<=n;i++)
        for(j=1;j<i-1;j++)
        {
            nr=v[i]-v[j];
            st=j+1;
            dr=i-1;
            while(st<dr)
            {
                med=(st+dr)/2;
                if(v[med]<nr)
                    st=med+1;
                else
                    dr=med;
            }
            med=(st+dr)/2;
            if(v[med]<nr)
                med++;
            cnt+=i-med;
        }
    printf("%d",cnt);
}