codeforce - little elephant and cards

#include<bits/stdc++.h>
using namespace std;
vector<pair<int,int> > v;
int main()
{
    int n,half;
    cin>>n;
    map<int,int>left,right;
    int x,y;
    if(n%2)
        half=n/2+1;
    else
        half=n/2;

    //cout<<half<<endl;
    for(int i=0; i<n; i++)
    {
        cin>>x>>y;
        v.push_back(make_pair(x,y));
        left[x]++;
        right[y]++;
        if(x==y)right[y]--;
    }
    int ans=n;
    for(int i=0; i<n; i++)
    {
        if(left[v[i].first]>=half)
        {
            ans=0;
            break;
        }
        if(left[v[i].first]<half)
        {
            if(right[v[i].first]+left[v[i].first]>=half)
            {
                ans=min(ans,half-left[v[i].first]);
            }
        }
        if(right[v[i].first]+left[v[i].first]>=half)
        {
            ans=min(ans,half-left[v[i].first]);
        }
        if(right[v[i].second]+left[v[i].second]>=half)
            ans=min(ans,half-left[v[i].second]);
        if(right[v[i].second]>=half)
            ans=min(half,ans);
    }
    if(ans==n)
        ans=-1;
    cout<<ans<<endl;
}