#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<map>
using namespace std;

const int maxn=10010;

class input
{
public:
    input& operator >> (int& x)
    {
        char c=' ';x=0;
        while(c<'0' || c>'9') c=getchar();
        while(c>='0' && c<='9') x=x*10+c-'0',c=getchar();
        return *this;
    }
}in;

map<int,int> mp;
int a[maxn],cur=0,n,m;

int main()
{
    freopen("leader.in","r",stdin);
    freopen("leader.out","w",stdout);
    in>>m>>n;
    for(int i=0,t;i<n;++i) {in>>t;if(!mp[t]) a[++cur]=t;mp[t]++;}
    n>>=1;
    for(int i=1;i<=cur;++i) if(mp[a[i]]>n)
    {
        cout<<a[i]<<endl;
        return 0;
    }
    printf("-1\n");
    return 0;
}