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

int v[801], triangles;

int main(){

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

    int N; scanf("%d", &N);

    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 = j + 1;
            while(v[i] + v[j] >= v[k] && k <= N) k++;
            triangles += k - j - 1;
         }
    }
    printf("%d", triangles);

    return 0;
}