//#include "pch.h"
//#include "stdafx.h"
#include <iostream>
#include <queue>
#include <vector>
#include <algorithm>
#include <math.h>
#include <string>
#include <cstring>

using namespace std;

/*-----------------------------------------------------------------------------
　ライブラリ
 -------------------------------------------------------------------------------*/
#if 0
// 3次元
vector<vector<vector<SDWORD>>> XXX(AAA, vector<vector<SDWORD>>(BBBB, vector<SDWORD>(CCC, -1)));
#endif

#if 0
// 降順ソート
sort(getValue.rbegin(), getValue.rend());
#endif

#if 0
// 2分探索
auto position = lower_bound(getValue.begin(), getValue.end(), 0);	// 0以上の要素位置を探す
int idx_lower = distance(getValue.begin(), position);				// 0以上の要素インデックス
int eraseNum = MIN(idx_lower, delCnt);								// 要素位置が個数になる
if (0 < eraseNum) {
	getValue.erase(getValue.begin(), getValue.begin() + eraseNum);
}
#endif

/*-----------------------------------------------------------------------------
　定義
 -------------------------------------------------------------------------------*/
#define REP(i, n) for (int (i) = 0 ; (i) < (int)(n) ; ++(i))
#define REPN(i, m, n) for (int (i) = m ; (i) < (int)(n) ; ++(i))
#define REP_REV(i, n) for (int (i) = (int)(n) - 1 ; (i) >= 0 ; --(i))
#define REPN_REV(i, m, n) for (int (i) = (int)(n) - 1 ; (i) >= m ; --(i))

#define INF				2e9
#define MOD				(1000 * 1000 * 1000 + 7)
#define MIN(a, b)		((a) < (b) ? a : b)
#define MAX(a, b)		((a) > (b) ? a : b)
#define CeilN(x, n)		(((((DWORD)(x))+((n)-1))/n)*n)	/* Nの倍数に切り上げ */
#define FloorN(x, n)	((x)-(x)%(n))					/* Nの倍数に切り下げ */
#define IsOdd(x)		(((x)&0x01UL) == 0x01UL)			
#define IsEven(x)		(!IsOdd((x)))						

#define ArrayLength(x)	( sizeof( x ) / sizeof( x[ 0 ] ) )
#define	ArrayEnd(a)		(&(a)[ArrayLength(a)])			
#define	ArrayLast(a)	(&(a)[ArrayLength(a) - 1])		
#define MAX_BYTE		(255)
#define MIN_BYTE		(0)
#define MAX_WORD		(65535)
#define MIN_WORD		(0)
#define MAX_SWORD		(32767)
#define MIN_SWORD		(-32768)
#define MAX_DWORD		(0xFFFFFFFF)
#define MIN_DWORD		(0)
#define	MAX_SDWORD		((SDWORD)0x7FFFFFFF)
#define	MIN_SDWORD		((SDWORD)0x80000000)
#define	MAX_QWORD		((QWORD)0xFFFFFFFFFFFFFFFF)
#define	MIN_QWORD		((QWORD)0x0000000000000000)
#define	MAX_SQWORD		((SQWORD)0x7FFFFFFFFFFFFFFF)
#define	MIN_SQWORD		((SQWORD)0x8000000000000000)

#define	BitSetV(Val,Bit)		((Val) |= (Bit))			
#define	BitClrV(Val,Bit)		((Val) &= (~(Bit)))			
#define	BitTstV(Val,Bit)		((Val) & (Bit))				
#define	BitInvV(Val,Bit)		((Val) ^= (Bit))			
#define	BitTstVVal(Val, Bit)	(BitTstV((Val), (Bit)) == (Bit))	

typedef short					SWORD;
typedef long					SDWORD;
typedef long long				SQWORD;
typedef unsigned short			WORD;
typedef unsigned long			DWORD;
typedef unsigned long long int	QWORD;
typedef pair<int, int> P;

/*-----------------------------------------------------------------------------
　パラメータ定義
 -------------------------------------------------------------------------------*/
#define N_MAX	(10)
#define K_MAX	(10)
#define M_MAX	(1000)
#define H_MAX	(1000)
#define W_MAX	(1000)
/*-----------------------------------------------------------------------------
　処理
 -------------------------------------------------------------------------------*/
// メイン
int main()
{
	int A, B;
	cin >> A >> B;

	if (A <= 9 && B <= 9) {
		cout << A * B;
	} else {
		cout << -1;
	}
	cout << endl;
	return 0;
}


Measured memory_bytes: 256