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 <iostream>
#include <algorithm>
#include <functional>
#include <vector>
#include <cstring>
using namespace std;

#define MAX_X 1500001

int n;
int x;
vector<int> p;

bool table[MAX_X];
vector<int> prime;

void init() {
    memset(table, 1, sizeof(table));
    table[0] = table[1] = false;
    for (int i = 2; i < MAX_X; i++) {
        if (table[i]) {
            prime.push_back(i);
            for (int j = i + i; j < MAX_X; j += i) {
                table[j] = false;
            }
        }
    }
}

bool cache[MAX_X];
bool cached[MAX_X];

bool can_make(int t) {
//    cout << t << endl;
    if (t == 0) return true;
    else if (t < 0) return false;
    if (cached[t]) return cache[t];

    bool can = false;
    for (int i = 0; i < p.size(); i++) {
        if (can_make(t-p[i])) {
            can = true;
            break;
        }
    }
    cache[t] = can;
    cached[t] = true;
    return can;
}

int main() {
    init();
//    for (int i = 0; i < prime.size(); i++) {
//        cout << prime[i] << ' ';
//    }

    while (cin >> n >> x, n || x) {
        memset(cache, 0, sizeof(cache));
        memset(cached, 0, sizeof(cached));

        p.clear();
        p.resize(n);
        for (int i = 0; i < n; i++) {
            cin >> p[i];
        }
        sort(p.begin(), p.end(), greater<int>());

        bool exist = false;

        int ub = prime.size()-1;
        int lb = 0;
        int mid;

        while (lb != ub - 1) {
            mid = (lb + ub) / 2;
            if (prime[mid] < x) {
                lb = mid;
            } else {
                ub = mid;
            }
        }

//        cout << "ub: " << ub << endl;
        for (int i = mid; 0 <= i; i--) {
            if (can_make(prime[i])) {
                cout << prime[i] << endl;
                exist = true;
                break;
            }
        }

        if (!exist) {
            cout << "NA" << endl;
        }

    }
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define FOR(i, s, n) for(int i = s; i < (int)n; i++)
#define per(i, n) for(int i = n; i >= 0; i--)
#define ROF(i, s, n) for(int i = s; i >= (int)n; i--)
#define FORIT(i, A) for (auto i : A)
#define PRINT(x) cout << (x) << "\n"
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define MP make_pair
#define EACH(i, n) for (__typeof((n).begin()) i = (n).begin(); i != (n).end(); ++i)
#define SZ(a) int((a).size())
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define CLR(a) memset((a), 0 ,sizeof(a))
#define NCLR(a) memset((a), -1 ,sizeof(a))
#define dump(x) cout << #x << " = " << (x) << "\n";
#define debug(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << "\n";
#define sq(n) (n) * (n)
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef priority_queue<int> maxpq;
typedef priority_queue< int, vector<int>, greater<int> > minpq;
static const double EPS = 1e-10;
static const double PI = acos( -1.0 );
static const int mod = 1000000007;
static const int INF = 1 << 25;
static const LL LL_INF = 1152921504606846976;
static const int dx[] = { -1, 0, 1, 0, 1, -1, 1, -1 };
static const int dy[] = { 0, -1, 0, 1, 1, 1, -1, -1 };

int dp[ 31 ][ 1000001 ];
bool is_pm[ 1000001 ];
int n, m;
VI _array;

int solve( int now, int many ) {
	if ( dp[ now ][ many ] >= 0 ) {
		return dp[ now ][ many ];
	}
	if ( now == n ) {
		if ( is_pm[ many ] ) {
			return dp[now][many] = many;
		}
		return dp[now][many] = 0;
	}
	int res = 0;
	for ( int i = 0; many + _array[ now ] * i <= m; i++ ) {
		res = max( res, solve( now + 1, many + _array[ now ] * i ) );
	}
	return dp[ now ][ many ] = res;
}

int main() {
	NCLR( is_pm );
	for ( int i = 2; sq( i ) <= 1000000; i += 2 ) {
		if ( is_pm[ i ] ) {
			for ( int j = i * i; j <= 1000000; j += i ) {
				is_pm[ j ] = false;
				if ( i != 2 ) {
					j += i;
				}
			}
		}
		if ( i == 2 ) {
			--i;
		}
	}
	is_pm[ 0 ] = is_pm[ 1 ] = false;
	while ( ~scanf( "%d %d", &n, &m ) && n && m ) {
		_array.resize( n );
		for ( int i = 0; i < n; i++ ) {
			scanf( "%d", &_array[ i ] );
		}
		sort( _array.rbegin(), _array.rend() );
		_array.erase( unique( _array.begin(), _array.end() ), _array.end() );
		n = _array.size();
		NCLR( dp );
		int ans = solve( 0, 0 );
		if ( ans ) {
			printf( "%d\n", ans );
		}
		else {
			printf( "NA\n" );
		}
	}
	return 0;
}

C++: #include <iostream>
#include <vector>
#include <set>
#include <algorithm>
#include <cmath>

using namespace std;
const int MAX = 1000000;
vector<int> Primes;
bool isPrime[MAX] = {0};

void sieve(){
    bool find[MAX] = {0};
    int i;
    for(i=2;i*i < MAX;i++){
        if(find[i]) continue;
        Primes.push_back(i);
        for(int j=i;j<MAX;j++){
            if(j%i == 0) find[j] = true;
        }
    }
    for(;i<MAX;i++){
        if(!find[i]) Primes.push_back(i);
    }
    for(int i=0;i<Primes.size();i++){
        isPrime[Primes[i]] = true;
    }
}

int main(){
    sieve();

    while(true){
        int n,x;
        cin >> n >> x;
        if(n==0 && x==0) return 0;
        vector<int> R(n);
        for(int i=0;i<n;i++){
            cin >> R[i];
        }

        set<int> S;
        S.insert(0);
        for(int i=0;i<R.size();i++){
            for(set<int>::iterator it=S.begin();it!=S.end();++it){
                int newe = *it + R[i];
                if(newe > x) continue;
                S.insert(newe);
            }
        }
        int maxn = -1;
        for(set<int>::iterator it=S.begin();it!=S.end();++it){
            if(isPrime[*it] && *it > maxn) maxn = *it;
        }
        if(maxn == -1) cout << "NA" << endl;
        else cout << maxn << endl;
    }
    return 0;
}