#include <cstdio>
#include <algorithm>
#define nmax 805

using namespace std;

short v[nmax];
int main()
{
    freopen("nrtri.in", "r", stdin);
    freopen("nrtri.out", "w", stdout);
    short n;

    scanf("%hd", &n);
    for(register short i=1;i<=n;i++)
        scanf("%hd", &v[i]);
    int sol=0;
    sort(v+1, v+n+1);
    for(register short i=1;i<=n-2;i++)
    {
        for(register short j=i+1;j<=n-1;j++)
        {
            short last=0;
            short k=j+1;
            int n1=n;
            while(k<=n1)
            {
                short mijl=k+(n1-k)/2;
                if(v[i]+v[j]>=v[mijl])
                {
                    last=mijl;
                    k=mijl+1;
                }
                else
                    n1=mijl-1;
            }
            if(last)
                sol+=last-j;
        }
    }
    printf("%d\n", sol);

    return 0;
}