#include using namespace std; #define ALL(x) x.begin(),x.end() #define rep(i,n) for(int i=0;i<(n);i++) #define debug(v) cout<<#v<<":";for(auto x:v){cout<bool chmax(T &a,const T &b){if(abool chmin(T &a,const T &b){if(b>n>>x; map mp; ll ans=0; rep(i,n){ ll a;cin>>a; ans+=2*mp[x-a]; if(a*2==x) ans++; mp[a]++; } cout<