#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=n;step;step>>=1)
        if(i-step>0&&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)
        {
            if(v[i]+v[j]<v[3])
                break;
            src=binarysearch(v[i]+v[j]);
            if(v[src]==v[i]+v[j])
                cnt+=src-j;
            else
                cnt+=src-j-1;
        }
    printf("%d",cnt);
}