#include <stdio.h>
#include <algorithm>

using namespace std;

int n;
int t[810];

int binary_search1(int st,int dr,int x)
{
    int sol=0;
    while (st<=dr) {
        int m=(st+dr)/2;
        if (t[m]<=x) sol=m,st=m+1; else
            dr=m-1;
    }

    return sol;
}

int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);

    scanf("%d",&n);

    for (int i=1;i<=n;i++) scanf("%d",&t[i]);

    sort(t+1,t+n+1); int sol=0;

    for (int i=1;i<=n;i++)
        for (int j=i+1;j<=n;j++) {
            int k=binary_search1(1,n,t[i]+t[j]);
            if (k>j) sol=sol+(k-j);
    }

    printf("%d",sol);

    return 0;
}