#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;

#define nmax 810

int n,v[nmax];

int cautbin(int val){

    int start=0, step=(1<<10);

    for( ; step; step>>=1){

        int index=start+step;
        if(index>n)continue;
        if(v[index]<=val)start=index;
    }

    return start;
}

int main(){

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

    scanf("%d", &n);

    int s=0;

    for(int i=1;i<=n;++i){

        scanf("%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 k=v[i]+v[j];

            int a=cautbin(k);

            if(a==i || a==j)continue;

            if(k>=v[a])
            {
                a=a-j;
                s=s+a;
            }
        }
    }

    printf("%d \n", s);
}