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])
		if n == 0 && x == 0 {
			break
		}
		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++: // clang-format off
#include <bits/stdc++.h>
#define int long long
#define main signed main()
#define loop(i, a, n) for (int i = (a); i < (n); i++)
#define rep(i, n) loop(i, 0, n)
#define forever for (;;)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define prec(n) fixed << setprecision(n)
template<typename A> using V = std::vector<A>;
template<typename A> using F = std::function<A>;
template<typename A, typename B> using P = std::pair<A, B>;
using pii = P<int, int>;
using vi = V<int>;
using vd = V<double>;
using vs = V<std::string>;
using vpii = V<pii>;
using vvi = V<vi>;
using vvpii = V<vpii>;
constexpr int INF = sizeof(int) == sizeof(long long) ? 1000000000000000000LL : 1000000000;
constexpr int MOD = 1000000007;
constexpr double PI = 3.14159265358979;
template<typename A, typename B> bool cmin(A &a, const B &b) { return a > b ? (a = b, true) : false; }
template<typename A, typename B> bool cmax(A &a, const B &b) { return a < b ? (a = b, true) : false; }
constexpr bool odd(const int n) { return n & 1; }
constexpr bool even(const int n) { return ~n & 1; }
template<typename T> std::istream &operator>>(std::istream &is, std::vector<T> &v) { for (T &x : v) is >> x; return is; }
template<typename A, typename B> std::istream &operator>>(std::istream &is, std::pair<A, B> &p) { is >> p.first; is >> p.second; return is; }
using namespace std;
// clang-format on

constexpr bool isPrime(const int n) {
  if (n == 1) return false;
  for (int i = 2; i * i <= n; i++) {
    if (n % i == 0) return false;
  }
  return true;
}

main {
  int n, x;
  while (cin >> n >> x, n) {
    vi v(n);
    cin >> v;
    vi dp(x + 1);
    dp[0] = true;
    for (auto &t : v) rep(i, x + 1 - t) dp[i + t] |= dp[i];
    for (int i = x; i > 0; i--) {
      if (dp[i] && isPrime(i)) {
        cout << i << endl;
        goto next;
      }
    }
    cout << "NA" << endl;
  next:;
  }
}

C++: #include <stdio.h>

int n,m[30];
/*
bool prime[1000000];
*/
bool c[1000000];

void saiki(int total){
	int i;
	if(total<=0){
		return;
	}
	
	for( i=0 ; i<n ; i++){
		total-=m[i];
		if(c[total]==1)continue;
		if(total>=0){
			c[total]=1;
		}
		saiki(total);
	}
}

int check(int prime){
	int flg=0,i;
	if(prime%2==0)return 0;
	for(i=3;i<prime;i+=2){
		if(prime%i==0){
			flg=1;
		}
	}
	if(flg==1)return 0;
	return 1;
}

int main(void)
{
	int i,j;
	//f
	/*
	prime[0]=1;
	prime[1]=1;
	for(i=3;i<1000000;i++){
		if(i%2==0){
			prime[i]=1;
		}
	}
	for(i=3;i<1000000;i++){
		if(prime[i]==0){
			for(j=(i+i);j<1000000;j+=i){
				prime[j]=1;
			}
		}
	}
	*/
	//
	while(1){
		int x;
		int flg=0;
		scanf("%d%d",&n,&x);
		if(n==0)break;
		
		for(i=0;i<n;i++){
			scanf("%d",&m[i]);
		}
		saiki(x);
		//
		for(i=0;i<x;i++){
			
			if(c[i]==1 && check(x-i)){
				flg=1;
				break;
			}
		}
		if(flg==1){
			printf("%d\n",x-i);
		}
		else puts("NA");
		for(i=0;i<1000000;i++){
			c[i]=0;
		}

for(;;);		//
	}
	
	
	return 0;
}

C++: #include <iostream>
#include <string>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstdlib>
using namespace std;

#define rep(i,a) for(int i = 0 ; i < a ; i ++)
#define loop(i,a,b) for(int i = a ; i < b ; i ++)

int dt[40];
bool prime[1000000];
bool dp[1000000];

int main(void){
	int n, x,lm;
	rep(i,100000){
		prime[i]=true;
	}
	for(int i=2;i<1000000;i++){
		for(int j=i*2;j<1000000;j+=i){
			prime[j]=false;
		}
	}

	while(cin>>n>>lm,n||lm){
		bool find = false;
		rep(i,100000){
			dp[i]=false;
		}
		dp[0] = 1;
		loop(i,0,n){
			cin>>dt[i];
			rep(j,lm){
				dp[j + dt[i]] |= dp[j];
			}
			
		}
		//rep(i,sizeof(okapon))if(okapon[i])cout<<i<<endl;
		for(int i = lm ; i >= 0 ; i --){
			if(i==1){cout<<"NA"<<endl;break;}
			if(dp[i] && prime[i]){cout<<i<<endl;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(){
    for(int i = 0; i <= MAX_X; ++i) is_prime_number[i] = true;
    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 <iostream>
#include <array>

#define MAX 1000000

void makePrime(auto& p_ptr, int data = MAX + 1)
{
    p_ptr[0] = p_ptr[1] = false;

    for (int i = 2; i * i < data; ++i) {
        for (int j = 2; j * i <= data; ++j) {
            p_ptr[j * i] = false;
        }
    }
}

int main()
{
    static std::array<bool, MAX> p;
    std::fill(p.begin(), p.end(), true);
    int price_num;
    int budget;

    makePrime(p);
    
    while (std::cin >> price_num >> budget) {
        if (price_num == 0 && budget == 0) break;
        
        //dp
        bool dp[MAX + 1] = {};
        int PriceData[price_num];

        for (int i = 0; i < price_num; ++i) {
            std::cin >> PriceData[i];
            dp[PriceData[i]] = true;
        }

        for (int i = 0; i < price_num; ++i) {
            for (int j = 0; j < MAX; ++j) {
                if (dp[j] && PriceData[i] + j <=  MAX) {
                    dp[PriceData[i] + j] = true;
                }
            }
        }
        
        int ans = 0; 
        for (int i = budget; i > 0; --i) {
            if (dp[i] && p[i]) {
                ans = i;
                break;
            }
        }

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