import std.algorithm;
import std.array;
import std.ascii;
import std.container;
import std.conv;
import std.math;
import std.numeric;
import std.range;
import std.stdio;
import std.string;
import std.typecons;
void log(A...)(A arg) { stderr.writeln(arg); }
int size(T)(in T s) { return cast(int)s.length; }

const X = 5000000;
void main() {
    auto isPrime = new bool[X + 1]; 
    auto nextPrime = new int[X + 1];
    auto prevPrime = new int[X + 1];
    {
        isPrime[] = true;
        isPrime[0] = isPrime[1] = false;
        int prev = 2; for (int j = 4; j <= X; j += 2) isPrime[j] = false;
        for (int i = 3; i <= X; i++) {
            if (isPrime[i]) {
                nextPrime[prev] = i;
                prevPrime[i] = prev;
                prev = i;
                for (int j = i + i; j <= X; j += i) {
                    isPrime[j] = false;
                }
            }
        }
        nextPrime[4999999] = X + 1;
        prevPrime[2] = 0 - 1;
    }
    int N; readf("%d\n", &N);
    auto A = readln.chomp.split(" ").map!(to!int).array;
    int set = 0; {
        foreach (a; A) {
            set |= 1 << a;
        }
    }
    int cur = 0;
    int ans = -1;
    int from = -1;
    for (int i = 2; i <= X; i++) {
        if (isPrime[i]) {
            auto s = to!string(i);
            int prev = cur;
            foreach (c; s) {
                int t = cast(int)(c - '0');
                cur |= 1 << t;
            }
            if ( (cur & set) == cur ) {
                if (from < 0) {
                    from = i;
                    if ( (cur & set) == set ) {
                        ans = max(ans, nextPrime[i] - prevPrime[i] - 2);
                    }
                }
            } else {
                if (from >= 0 && prev == set) {
                    ans = max(ans, i - prevPrime[from] - 2);
                }
                from = -1;
                cur = 0;
            }
        }
    }
    if (from >= 0 && cur == set) {
        ans = max(ans, X - prevPrime[from] - 2);
    }
    writeln(ans);
}