#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
int v[800+5],n;
void cautare(int i,int j,int&poz){
    int prod=1<<10;
    while(prod>=1){
        if(poz+prod<n && v[poz+prod]<=v[i]+v[j])
            poz+=prod;
        prod/=2;
    }

}
int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    int poz,nrtri=0;
    scanf("%d",&n);
    for(int i=0;i<n;i++)
        cin>>v[i];
    sort(v+0,v+n);
    for(int i=0;i<n-1;i++){
        int k;
        k=i+2;
        for(int j=i+1;j<n;j++){
            while(k<n && v[i]+v[j]>=v[k])
                k++;
            if(j+1<=k-1)
                nrtri+=k-j-1;
        }
    }
    cout<<nrtri;
    return 0;
}