#include<cstdio>
#include<algorithm>

using namespace std;

const int nmax=805;

int n,v[nmax];

inline int binarysearch(int x)
{
    int i,step;
    for(step=1;step<=n;step<<=1);
    for(i=0;step;step>>=1)
        if(i+step<=n&&v[i+step]<=x)
            i+=step;
    return i;
}

int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    int i,j,src,cnt=0;
    scanf("%d",&n);
    for(i=1;i<=n;++i)
        scanf("%d",&v[i]);
    sort(v+1,v+n+1);
    for(i=1;i<n;++i)
        for(j=i+1;j<n;++j)
        {
            src=binarysearch(v[i]+v[j]);
            cnt+=src-j;
        }
    printf("%d",cnt);
}