# include <algorithm>
using namespace std;

const char FIN[] = "nrtri.in", FOU[] = "nrtri.out" ;

int V[805] ;
int N, sol, aux ;

inline int cb ( int val ) {
    int rez = 0, cnt, i ;

    for ( cnt = aux, i = 0; cnt; cnt >>= 1 ) {
        if ( i + cnt <= N && V[i + cnt] <= val ) {
            i += cnt;
        }
    }

    return i ;
}

int main() {
    freopen ( FIN, "r", stdin ) ;
    freopen ( FOU, "w", stdout ) ;

    scanf ( "%d", &N ) ;

    for ( int i = 1; i <= N; ++i ) {
        scanf ( "%d", &V[i] ) ;
    }

    sort ( V + 1, V + N + 1 ) ;

    for ( aux = 1; aux <= N; aux <<= 1 ) ;

    for ( int i = 1; i < N; ++i ) {
        for ( int j = i + 1; j <= N; ++j ) {
            sol += cb ( V[i] + V[j] ) - j ;
        }
    }

    printf ( "%d", sol ) ;

    return 0;
}