#include <bits/stdc++.h>
using namespace std;

#define INF 2139062143
#define LINF 9187201950435737471
#define mem(a,v) memset(a,v,sizeof(a))
#define maxn 100010
#define rep(i, a, b) for (int i = (a); i <= (b); ++i)
#define red(i, a, b) for (int i = (a); i >= (b); --i)
#define pb push_back
#define eps 1e-6
#define ll long long
#define max(a,b) (a>b?a:b)
#define min(a,b) (a<b?a:b)
typedef pair<int, int> pp;

int n,k,T;
int a[maxn];
int b[maxn];
map<int,int> num;
int pre[maxn];
inline int findx(int u){
    return lower_bound(b+1,b+1+b[0],u) - b;
}
int main() {
//    ios::sync_with_stdio(false);cout.setf(ios::fixed);cout.precision(6);
#ifdef LOCAL
    freopen("/Users/huangqingwei/Documents/clionworkspace/hqw/input.txt", "r", stdin);
//    freopen("/Users/huangqingwei/Documents/clionworkspace/hqw/output.txt", "w", stdout);
#endif
    while(~scanf("%d%d%d",&n,&k,&T))
    {
        num.clear();
        mem(pre,0);
        rep(i,1,n)
            scanf("%d",a+i);
        rep(i,1,n)
            b[i] = a[i];
        sort(b+1,b+1+n);
        b[0] = unique(b+1,b+1+n) - b - 1;
        rep(i,1,n)
            num[findx(a[i])]++;
        red(i,b[0],1)
            pre[i] = pre[i+1] + num[i];
        int l = 1, r = b[0], mid;
        while(l<r)
        {
            mid = l + ((r-l+1)>>1);
            if(pre[mid]>=k)
                l = mid;
            else
                r = mid - 1;
        }
        if(pre[l]>k)
        {
            if(T==0)
            {
                puts("-1");
            }
            else if(b[l]==0)
            {
                printf("%d\n",k-pre[l+1]);
            }
            else if(b[l]==T)
            {
                printf("%d\n",pre[l]-k);
            }
            else
            {
                printf("%d\n",min(k-pre[l+1],pre[l]-k));
            }
        }
        else if(pre[l]==k)
        {
            puts("0");
        }
        else
        {
            puts("-1");
        }
    }



#ifdef LOCAL
    cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
#endif
    return 0;
}