{\rtf1\ansi\ansicpg1250\deff0\deflang1048{\fonttbl{\f0\fswiss\fcharset0 Arial;}}
{\*\generator Msftedit 5.41.21.2508;}\viewkind4\uc1\pard\lang1033\f0\fs20 #include <cstdio>\par
#define deb(n) fprintf(stderr,"%d ",(n));\par
#define DN 9005\par
\par
int n,v[DN],aparitii[DN];\par
\par
int main()\par
\{\par
\tab freopen("medie.in","r",stdin);\par
\tab freopen("medie.out","w",stdout);\par
\tab int i;\par
\tab scanf("%d",&n );\par
\tab for(i=1; i<=n;++i) \{\par
\tab     scanf("%d",&v[i] );\par
\tab     ++aparitii[v[i]];\par
\tab\}\par
\tab int rez=0;\par
\tab for(i=2; i<=n;++i) for(int j=1; j<i; ++j) \{\par
\tab     int sum=v[i]+v[j];\par
\tab     if(0==sum%2)\{\par
\tab         rez+=aparitii[sum/2];\par
\tab         if(v[i]==v[j]) rez-=2;\par
\tab     \}\par
\tab\}\par
\tab printf("%d",rez);\par
\tab return 0;\par
\}\par
}