#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int a[10005];
int b[10005];
bool cmp(int c,int d){
    return c>d;
}
int main(){
    int n,num;
    int temp;
    while(scanf("%d",&n)!=EOF){
        memset(a,0,sizeof(a));
        memset(b,0,sizeof(b));
        num=0;
        for(int i=0;i<n;i++)
        {
            scanf("%d",&temp);
            a[temp]++;
            //printf("%d %d %d %d\n",a[0],a[1],a[2],a[3]);
        }
        for(int j=0;j<=10001;j++)
        b[j]=a[j];
        sort(a,a+10001,cmp);
    //    printf("%d %d %d %d\n",a[0],a[1],a[2],a[3]);
        for(int i=1;i<=10001&&a[i]!=0;i++){
            num+=a[i];//printf("%d\n",num);
        }
        
        
        if(num<a[0]){
            int k=0;
        while(a[0]!=b[k]){
            k++;
        } 
        printf("%d\n",k);
         
    }
    else printf("-1\n");
    
} }