#include //ios::sync_with_stdio(false);cin.tie(0);cout.tie(0); //clock_t start=clock();clock_t end=clock();cout<<(double)(end-start)/CLOCKS_PER_SEC< pii; typedef pair ppii; typedef pair pipi; typedef pair pll; typedef pair ppll; typedef pair plpl; typedef pair P; typedef tuple tl; typedef pair pdd; typedef vector> mat; ll mod=1000000007; ll mod2=998244353; ll mod3=1000003; ll mod4=998244853; ll mod5=1000000009; ll inf=1LL<<60; double pi=3.141592653589793238462643383279L; double eps=1e-14; #define rep(i,m,n) for(ll i=m;i=m;i--) #define srep(itr,st) for(auto itr=st.begin();itr!=st.end();itr++) #define mrep(itr,mp) for(auto itr=mp.begin();itr!=mp.end();itr++) #define Max(a,b) a=max(a,b) #define Min(a,b) a=min(a,b) int dh[4]={1,-1,0,0}; int dw[4]={0,0,1,-1}; int ddh[8]={-1,-1,-1,0,0,1,1,1}; int ddw[8]={-1,0,1,-1,1,-1,0,1}; struct custom_hash { static uint64_t splitmix64(uint64_t x) { // http://xorshift.di.unimi.it/splitmix64.c x += 0x9e3779b97f4a7c15; x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9; x = (x ^ (x >> 27)) * 0x94d049bb133111eb; return x ^ (x >> 31); } size_t operator()(uint64_t x) const { static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count(); return splitmix64(x + FIXED_RANDOM); } }; #define umh unordered_map ll gcd(ll a,ll b){ if(a0){ if(k&1)ret*=now; now*=now; k/=2; } return ret; } ll beki(ll n,ll k,ll md){ ll ret=1; ll now=n; now%=md; while(k>0){ if(k%2==1){ ret*=now; ret%=md; } now*=now; now%=md; k/=2; } return ret; } ll gyaku(ll n,ll md){ return beki(n,md-2,md); } ll popcount(ll n){ ll ret=0; ll u=n; while(u>0){ ret+=u%2; u/=2; } return ret; } int main(){ ios::sync_with_stdio(false);cin.tie(0); int n;cin>>n; int a[2*n]; multiset st; rep(i,0,2*n){ cin>>a[i]; st.insert(a[i]); } int ans=0; for(;;){ if(st.size()==0)break; auto itr=st.end(); itr--; int now=*itr; if(now<=0)break; auto itr2=st.lower_bound(-now+1); if(*itr2==now)break; ans++; st.erase(itr); st.erase(itr2); } int anss=ans; st.clear(); rep(i,0,2*n)st.insert(a[i]); ans=0; for(;;){ if(st.size()==0)break; auto itr=st.begin(); int now=*itr; if(now>=0)break; auto itr2=st.lower_bound(-now); itr2--; if(*itr2==now)break; ans++; st.erase(itr); st.erase(itr2); } cout<=0)used[a[i]]++; } rep(i,0,2*n){ if(a[i]<0){ if(used[-a[i]]>0){ ans++; used[-a[i]]--; } } } ans+=used[0]/2; cout<