#include<fstream>
using namespace std;
ifstream fin("elmaj.in");
ofstream fout("elmaj.out");
int a[1000003];
int main()
{int n,i,k,max=0,j;
fin>>n;
for(i=1;i<=n;i++)
    fin>>a[i];
for(i=1;i<=n-1;i++)
{k=1;
    if(a[i]!=0)
    for(j=i+1;j<=n;j++)
    if(a[j]==a[i])
    {k++;
    a[j]=0;
    }
    if(k>max)
        max=k;

}
if(max>=n/2+1)
    fout<<max;
else
    fout<<-1;
}