#include<stdio.h>
int m,n,m1,num[25000]={0},n1,max,i,i1,ma;
/*void find()
{
	for (i=0;i<25000;i++) 
	{
		scanf("%d",&n1);
		num[n1]++;
		if (n1>ma) ma=n1;
	}
	max=0;
	for (i=0;i<=ma;i++)
	{
		if (num[i]>max) 
		{
			max=num[i];
			i1=i;
		}
	}
}*/

int main()
{
	int m,n,m1,num[25000]={0},n1,max,i,i1,ma;
	freopen("leader.in","r",stdin);
	freopen("leader.out","w",stdout);
	
	scanf("%d %d",&n,&m);
	m1=m/2;
	ma=0;
	if (n<25000) 
	{
		for (i=0;i<m;i++) 
		{
			scanf("%d",&n1);
			num[n1]++;
			if (n1>ma) ma=n1;
		}
		max=0;
		for (i=0;i<=ma;i++)
		{
			if (num[i]>max) 
			{
				max=num[i];
				i1=i;
			}
		}
		if (max>=m1) printf("%d",i1);
		else printf("-1");
	}
	
	fclose(stdin);
	fclose(stdout);
	return 0;
}