#include <bits/stdc++.h>
using namespace std;
const int nmax=1e6+1;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
bool f[nmax+5];
fill(f,f+nmax+5,true);
f[0]=f[1]=false;
for (int i=2;i*i<=nmax;++i) {
if (f[i]) {
for (int j=i*i;j<=nmax;j+=i)
f[j]=false;
}
}
long long n,s=0,a1=LLONG_MAX,c=LLONG_MIN;
cin>>n;
for (int i=0;i<n;++i) {
long long a2;
cin>>a2;
s+=a2;
if (f[i+1]) c=max(c,s-a1);
if (f[i+2]) a1=min(a1,s);
}
cout<<c;
return 0;
}

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const ll nmax = 1e6 + 1;

bool f[nmax + 5];
void snt()
{
    memset (f , true , sizeof(f));
    f[0] = f[1] = false;
    for (int i = 2; i <= sqrt(nmax); ++i)
    if (f[i]) for (ll j = i * i; j <= nmax; j += i)
    f[j] = false;
}
ll ans = 1e18, cnt = -1e18, n, s = 0;
int main()
{

 ios::sync_with_stdio(false);
 cin.tie(nullptr);

 snt();
 cin >> n;
 for (ll i = 0; i < n; ++i)
 {
    ll a;
    cin >> a;
    s += a;
    if (f[i + 1]) cnt = max(cnt , s - ans);
    if (f[i + 2]) ans = min(ans , s);
 }
 cout << cnt;
 return 0;
}