#include<fstream>
#include<algorithm>
using namespace std;
int v[1000];
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int main ()
{
    int n,x,y,pos,msk,a,s=0;
    in>>n;
    for(int i=1; i<=n; i++){
        in>>v[i];
    }
    sort(v+1,v+n+1);
    x=v[n];
    y=v[n-1];
    while(y>=1)
    {
    a=x-y;
    pos=0;
    for(msk=1<<20;msk>0;msk/=2)
        if(pos+msk<=n && v[pos+msk]<=a)
        pos+=msk;
        if(pos!=0)
        {s+=y-pos;}
    x--;
    y--;
    }
    out<<s;
    return 0;
}