Go: package main

import (
	"bufio"
	"os"
	"strings"
	"strconv"
	"fmt"
	)

var scanner = bufio.NewScanner(os.Stdin)

func main() {
	for scanner.Scan() {
		buf := strings.Split(scanner.Text(), " ")
		n, _ := strconv.Atoi(buf[0])
		x, _ := strconv.Atoi(buf[1])
		prime_table := make([]int, 1000001)
		prime_table[0] = -1
		prime_table[1] = -1
		for i := 2; i < 1000001; i++ {
			if prime_table[i] != -1 {
				prime_table[i] = 1
				for j := 2*i; j < 1000001; j += i {
					prime_table[j] = -1 // -1 means "not prime"
				}
			}
		}
		dp := make([]int, x+1)
		dp[0] = 1
		menu := make([]int, n)
		for i := 0; i < n; i++ {
			scanner.Scan()
			menu[i], _ = strconv.Atoi(scanner.Text())
		}
		for i := 0; i < n; i++ {
			for j := 0; j <= x; j++ {
				if menu[i] <= j && dp[j-menu[i]] != 0 {
					// log.Println(dp)
					dp[j] = 1
				}
			}
		}
		flag := true
		for j := x; j >= 0; j-- {
			if prime_table[j] == 1 && dp[j] == 1 {
				flag = false
				fmt.Println(j)
				break
			}
		}
		if flag {
			fmt.Println("NA")
		}
	}
}

C++: #include <stdio.h>
#include <algorithm>
using namespace std;
int n, x, a[30]; bool dp[1000001], prime[1000001];
int main() {
	prime[0] = true, prime[2] = true;
	for(int i = 3; i <= 1000000; i += 2) prime[i] = true;
	for(int i = 3; i <= 1000; i++) {
		if(!prime[i]) continue;
		for(int j = i; i * j <= 1000000; j += 2) prime[i * j] = false;
	}
	while(scanf("%d%d", &n, &x), n) {
		for(int i = 0; i < n; i++) scanf("%d", &a[i]); sort(a, a + n);
		for(int i = 0; i < x; i++) dp[i + 1] = false; dp[0] = true;
		for(int i = 1; i <= x; i++) {
			for(int j = 0; j < n && i >= a[j]; j++) {
				if(dp[i - a[j]]) {
					dp[i] = true; break;
				}
			}
		}
		for(int i = x; i >= 0; i--) {
			if(dp[i] && prime[i]) {
				printf(i ? "%d\n" : "NA\n", i); break;
			}
		}
	}
}

C++: #include <iostream>
#include <algorithm>
#include <limits>
#include <cstring>

constexpr int MAX_X = 1000001;
constexpr int MAX_N = 31;

int n, x, values[MAX_N];
bool is_prime_number[MAX_X] = {true};

void initialize();

void solve();

int main(){
   initialize();
   while(true){
       memset(values, 0, MAX_N);

       std::cin >> n >> x;
       
       if(n + x == 0) break;
       
       for(int i = 0; i < n; ++i)
           std::cin >> values[i];

       solve();
   }
}

void initialize(){
    memset(is_prime_number, true, MAX_X);
    is_prime_number[0] = false, is_prime_number[1] = false;
    for(int i = 2; i * i <= MAX_X; ++i){
        if(is_prime_number[i]){
            for(int j = i + 1; j < MAX_X; ++j){
                if(j % i == 0)
                    is_prime_number[j] = false;
            }
        }
    }
}

void solve(){
   int ans = 0;
   int dp[MAX_X];
   memset(dp, 0, MAX_X);

   /*
   std::cout << "x : " << x << std::endl << "n : " << n << std::endl;
   for(int i = 0; i < (x > 1000 ? 1000 : x); ++i){
       std::cout << i << " dp : " << dp[i] << std::endl;
   }
   */

   for(int i = 1; i <= x; ++i){
       int res = 0;
       for(int j = 0; j < n; ++j){
           if(values[j] <= i){
               res = std::max(dp[i - values[j]] + values[j], res);
           }
       }
       dp[i] = std::max(dp[i], res);
       if(is_prime_number[dp[i]]){
           ans = std::max(dp[i], ans);
       }
   }

   if(ans != 0){
       std::cout << ans << std::endl;
   }
   else{
       std::cout << "NA" << std::endl;
   }

}

C++: #include <bits/stdc++.h>
using namespace std;
#define all(c) (c).begin(),(c).end()
#define rep(i,n) for(int i=0; i<(int)(n); i++)
#define rrep(i,n) for(int i=(int)(n)-1; i>=0; i--)
#define REP(i,m,n) for(int i=(int)(m); i<(int)(n); i++)
#define iter(c) __typeof((c).begin())
#define tr(it,c) for(iter(c) it=(c).begin(); it!=(c).end(); it++)
#define pb(a) push_back(a)
#define mp(a,b) make_pair(a,b)
#define pr(a) cout << (a) << endl
#define PR(a,b) cout << (a) << " " << (b) << endl
#define F first
#define S second
typedef long long ll;
typedef pair<int,int> P;
const int MAX=1000000001;
const ll MAXL=1000000000000000001LL;
const ll mod=1000000007;
int dx[4]={-1,0,1,0},dy[4]={0,-1,0,1};

vector<int> sieve(int n) {
  vector<int> p(n);
  for(int i=2; i<n; i++) p[i]=i;
  for(int i=2; i*i<n; i++) {
    if(p[i]) {
      for(int j=i*i; j<n; j+=i) p[j]=0;
    }
  }
  return p;
}

int main() {
  vector<int> prime=sieve(1000001);
  int n,m;
  while(cin >> n >> m && (n||m)) {
    bool dp[m+1];
    memset(dp,false,sizeof(dp));
    dp[0]=true;
    int ans=-1;
    rep(i,n) {
      int x;
      cin >> x;
      rep(j,m) {
	if(dp[j] && j+x<=m) {
	  dp[j+x]=true;
	  if(prime[j+x]) ans=max(ans,j+x);
	}
      }
    }
    if(ans==-1) pr("NA");
    else pr(ans);
  }
  return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <cstring>

constexpr int MAX_N = 31, MAX_C = 1000001;
int n, max;
int cost[MAX_N];
int dp[MAX_C];
bool prime_num[MAX_C];

int main() {
	while (1) {
		std::cin >> n >> max;
		if (n + max == 0)
			break;
		std::memset(prime_num, false, sizeof(prime_num));
		std::memset(dp, 0, sizeof(dp));
		for (int i = 0; i < n; ++i)
			std::cin >> cost[i];
		for (int i = 2; i * i <= max; ++i) {
			if (!prime_num[i]) {
				for (int j = 2; i*j <= max; ++j)
					prime_num[i*j] = true;
			}
		}
		int ans = 0;
		for (int i = 1; i <= max; ++i) {
			dp[i] = dp[i - 1];
			for (int j = 0; j < n; ++j) {
				if (i >= cost[j]) {
					if (!prime_num[dp[i - cost[j]] + cost[j]])
						ans = dp[i - cost[j]] + cost[j];
					dp[i] = std::max(dp[i], dp[i - cost[j]] + cost[j]);
				}
			}
		}
		if (!ans)
			std::cout << "NA" << std::endl;
		else
			std::cout << ans << std::endl;
	}
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
const int XMAX = 1000000;
const int SQRTXMAX = sqrt(XMAX);

bool is_prime[XMAX + 1];
bool dp[XMAX + 1];
int cost[30];

int main() {
  // prime
  memset(is_prime, true, sizeof(is_prime));
  is_prime[0] = is_prime[1] = false;
  for (int i = 2; i <= SQRTXMAX; i++) {
    if (is_prime[i]) {
      int current = i * i;
      for (int j = i * i; j <= XMAX; j += i) {
        is_prime[j] = false;
      }
    }
  }

  int n, x;
  while (cin >> n >> x, n) {
    for (int i = 0; i < n; i++) cin >> cost[i];

    // dp
    int r = 0;
    dp[0] = true;
    for (int i = 1; i <= x; i++) {
      dp[i] = false;
      for (int j = 0; j < n; j++) {
        int k = i - cost[j];
        if (k >= 0 && dp[k]) {
          dp[i] = true;
          if (is_prime[i]) r = i;
          break;
        }
      }
    }

    if (r == 0) {
      cout << "NA" << endl;
    } else {
      cout << r << endl;
    }
  }
  return 0;
}

C++: #include<iostream>
using namespace std;

int main(){
  int n,x,i,j;
  int d[30];
  bool can[1000001];

  for(;;){
    cin >> n >> x;
    if(!n && !x)break;

    for(i=0;i<n;i++)cin >> d[i];
    for(i=1;i<=x;i++)can[i] = false;
    can[0] = true;

    for(i=0;i<n;i++){
      for(j=0;j+d[i]<=x;j++){
	if(can[j])can[j+d[i]] = true;
      }
    }

    if(!(x&1))x--;
    for(i=x;i>=0;i-=2)
      if(can[i] && i&1){
	bool f=true;
	for(j=3;j*j<=i;j+=2)
	  if(!(i%j)){
	    f = false;
	    break;
	  }
	if(f)break;
      }
    if(i<0)cout << "NA" << endl;
    else cout << i << endl;
  }
}