#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

#define TABLE_SIZE 1000001

bool is_prime[TABLE_SIZE+1];
int n, m;

void makePrimeTable(void) {
  for (int i = 2; i <= TABLE_SIZE; ++i)
    is_prime[i] = true;
  for (int i = 2; i * i <= TABLE_SIZE; ++i)
    if (is_prime[i])
      for (int j = i * 2; j <= TABLE_SIZE; j += i)
        is_prime[j] = false;
}



int main(int argc, char const *argv[]) {
  int n, p;
  makePrimeTable();
  while (cin >> n >> p && ~n) {
  vector < int > prime, matsu;
    for (int i = n + 1; i <= n + 1000; ++i)
      if (is_prime[i]) prime.push_back(i);
    for (int i = 0; i < prime.size(); ++i)
      for (int j = i; j < prime.size(); ++j)
          matsu.push_back(prime[i] + prime[j]);
    sort(matsu.begin(), matsu.end());
    cout << matsu[p-1] << endl;
  }
  return 0;
}