纯模拟

#pragma GCC optimize(3,"Ofast","inline")
#include<bits/stdc++.h>
using namespace std;
long n,m,i,s,ma,a[10050];
long read()
{
	long x=0,f=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){
		if(ch=='-')f=-1;
		ch=getchar();
	}
	while(ch>='0'&&ch<='9')
	{
		x=x*10+(ch-'0');
		ch=getchar();
	}
	return x*f;
}
void write(long x) {
	if(x<0){
		putchar('-');
		write(-x);
		return;
	}
	if(x>=10)write(x/10);
	putchar(x%10+'0');
}
int main()
{
   n=read(),m=read();
   for(i=1;i<=m;i++)a[i]=read();
   sort(a+1,a+m+1);
   s=1;
   for(i=2;i<=m;i++)
      if(a[i]==a[i-1])s++;
      else{
         if(s>m/2){
            write(a[i-1]);
            return 0;
         }
         s=1;
      }
   if(s>m/2){
      write(a[m]); 
   }
   else write(-1);
	return 0;
}