#include<iostream>
#include<fstream>
#include<math.h>
#include<bitset>
using namespace std;

#define NMAX 100001
#define VMAX 1000001

int v[NMAX],nr[NMAX],d[NMAX],p[NMAX];
bitset <VMAX> viz;

void ciur()
{
	int i,j;
	for(i=2;i<=VMAX-1;i++) 
		if(viz[i]==0) {
			p[++p[0]]=i;
			for(j=i+i;j<=VMAX-1;j=j+i)
				viz[j]=1;
		}
}

inline int BIT(int x, int nr)
{
	return (x & (1<<nr))!=0;
}

int main ()
{
	int i,j,stop,k,prod,l,count,n;
	long long sol;
	ifstream f("pairs.in");
	ofstream g("pairs.out");
	f>>n;
	for(i=1;i<=n;i++)
		f>>v[i];
	f.close();
	sol=1LL*n*(n-1)/2;
	ciur();
	g<<sol;
	g.close();
	return 0;
}