import std.stdio, std.string, std.conv
	,std.array,std.algorithm, std.range
	,std.math;


void main(){
	readln();
	auto Ao = readln().strip().split().map!(to!int)();
	int A;
	foreach(int t; Ao) {
		A += 1<<t;
	}

	bool is_prime[5000001];

	void Eratosthenes(int lim){
		is_prime[] = true;
		is_prime[0] = false;
		is_prime[1] = false;
		for(int p=2; p*p<=lim; p++) {
			if(is_prime[p]){
				for(int k=p*p; k<=lim; k+=p) is_prime[k] = false;
			}
		}
	}

	Eratosthenes(5000000);

	int st = 1;
	int maxr = 0;
	bool ing = true;
	int At = A;
	foreach(int i; 1 .. 5000001) {
		if(is_prime[i]) {
			bool inc = true;
			char[] tpr = i.to!(char[]);
			auto a = tpr.map!(a => a-'0')().array;
			a.sort().uniq();

			int tt = 0;
			foreach(int t; a) {
				tt |= 1<<t;
			}

			foreach(int t; a) {
				if(A&1<<t) {
				} else {
					inc = false;
					break;
				}
			}

			if(ing) {
				if(inc) {
					At &= ~tt;
				} else {
					if(!At) {
						maxr = max(maxr, i - 1 - st);
					}
					ing = false;
				}
			} else {
				if(inc) {
					At = A;
					At &= ~tt;
					ing = true;
					st = i;
				}
			}
		} else if(!ing) {
			At = A;
			ing = true;
			st = i;
		}
	}

	if(ing && !At)
		maxr = max(maxr, 5000000 - st);
	
	writeln( maxr==0?-1:maxr );
}