#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define endl '\n'
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define rep2(i,a,b) for(int i=int(a);i<int(b);i++)
#define pb emplace_back
#define all(x) (x).begin(),(x).end()
int mod=1e9+7;
int mod2=998244353;
const int INF=1e9;

signed main(){
	vector<ll> iss(1000001,1);
	iss[0]=0;
	iss[1]=0;
	rep2(i,2,1000001){
		if(iss[i]){
			for(ll j=i*2;j<1000001;j+=i){
				iss[j]=0;
			}
		}
	}

	ll n,p;
	while(1){
		cin>>n>>p;
		if(n==-1&&p==-1)break;

		vector<ll> slist;
		rep2(i,n+1,n+1000001)if(iss[i])slist.pb(i);
		vector<ll> wlist;
		ll si=slist.size();
		si=min(si,100LL);
		rep(i,si){
			rep2(j,i,si){
				wlist.pb(slist[i]+slist[j]);
			}
		}
		sort(all(wlist));
		//rep(i,30)cout<<wlist[i]<<endl;
		cout<<wlist[p-1]<<endl;
	}
}

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