#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ar array
const ll linf = 1e15;
#define int long long
void solve() {
int n, p;
cin >> n >> p;
vector<int> a(n),b(n),k(p + 1);
for (int i = 0; i < p;i++) {
cin >> k[i];
if (i) k[i] += k[i - 1];
}
for (int i = 0; i <n;i++) cin >> a[i] >> b[i];
k[p] = k[ p- 1];
ll ans = 0,mx = 0;
//for (int i = 0; i < p;i++) cerr << k[i] << " ";
function<ll(int,int,int)> brute = [&](int id,int id2,ll cur)->ll{
//cerr << id << " " << id2 << " " << k[id2] << " " << cur << "\n";
if (id == k[id2]) {
// cerr << cur << "\n";
return max(mx,cur);
}
for (int v = a[id]; v <= b[id];v++) {
mx = max(mx,brute(id + 1,id2,(cur | v)));
}
return mx;
};
function<void(int,int)> brute2 = [&](int id,ll val){
// cerr << val << " "<< id << "\n";
if (id == p) {
// cerr << val << " ";
ans = max(ans,val);
return;
}
if (id == -1) {
mx = 0;
ll vv = brute(0,0,0);
// cerr << vv << "\n";
brute2(id + 1, vv);
}
else if (id + 1 == p) {
ans = max(ans,val);
//cerr << val << " " <<id << " ";
return;
}
else mx = 0,brute2(id + 1,(val & brute(k[id],id + 1, 0)));
};
brute2(-1,0);
cout << ans;
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int t = 1;
// cin >> t;
while (t--) {
solve();
cout << "\n";
}
return 0;
}
