#include<algorithm>
#include<cstdio>
using namespace std;
int v[810], n, ct;
int cautbin(int a, int b)
{
    int start, step = 1;
    int val = a + b;
    start = 0;
    for(; step <= n; step <<= 1);
    for(; step; step >>= 1)
    {
        int index = start + step;
        if(index > n) continue;
        else
        {
            if(v[index] <= val) start = index;
        }
    }
    return start;
}
int main()
{
    FILE* in = fopen("nrtri.in", "r");
    FILE* out = fopen("nrtri.out", "w");
    fscanf(in, "%d", &n);
    for(int i = 1; i <= n; ++i)
    {
        fscanf(in, "%d", &v[i]);
    }
    sort(v + 1, v + n + 1);
    for(int i = 1; i <= n - 2; ++i)
    {
        for(int j = i + 1; j <= n - 1; ++j)
        {
            int z = cautbin(v[i], v[j]);
            ct += z - j;
            //fprintf(out, "%d %d\n", z, j);
        }
    }
    fprintf(out, "%d", ct);
}