#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define ll long long 
using namespace std;
ll a[10010];
int main(){
	freopen("leader.in","r",stdin);
	freopen("leader.out","w",stdout);
	ll n,m,i,tot=1,ans=0,ansj;
	scanf("%d%d",&n,&m);
	for(i=1;i<=m;i++) scanf("%d",&a[i]);
	sort(a+1,a+1+m);
	for(i=2;i<=m;i++){
		if(a[i]!=a[i-1]){
			if(ans<tot){
				ans=tot;
				tot=1;
				ansj=a[i-1];
			}
		}
		else tot++;
	}
	if(ans<tot){
		ans=tot;
		tot=1;
		ansj=a[m];
	}
	printf("%lld\n",ans>m/2?ansj:-1);
	return 0;
}