#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <ctype.h>
#include <quadmath.h>
#include <math.h>
// Yukicoder №293 4>7の世界
// https://yukicoder.me/problems/no/293
// ***********************
// for debug
#define DEBUGw

#define NOP do{}while(0)
#ifdef DEBUG
#define TRACE(...) do{printf(__VA_ARGS__);fflush(stdout);}while(0)
#define TRACECR do{putchar_unlocked('\n');fflush(stdout);}while(0)
#else
#define TRACE(...) NOP
#define TRACECR NOP
#endif

#define PRINCR putchar_unlocked('\n')
#define NOCR(strig) do{char *p;p=strchr(strig,'\n');if(p)*p='\0';}while(0)
// The out-of-date function
#define	asctime(...)	asctime_s(...)
#define	ctime(...)		ctime_s(...)
#define	strlen(a)	mystr_len(a)
//#define	fopen(...)		fopen_s(...)
//#define	freopen(...)	freopen_s(...)
//#define	rewind(a)		fseek(a,0L,SEEK_SET)
//#define	setbuf(a,b)		setvbuf(a,b,_IOFBF,BUFSIZ)

// for stdio
#define GETLINE(str) do{char *p;fgets(str,sizeof(str),stdin);p=strchr(str,'\n');if(p)*p='\0';}while(0)
#define mygc(c) (c)=getchar()
static char *GETWORD( char* str );
static char *GETWORD(char* str) {char c;char *cp;cp=&str[0];c=getchar_unlocked();while( c != EOF ){if((c==' ')||( c=='\n')) break;*cp++=c;c=getchar_unlocked();}*cp='\0';return &str[0];}
#define	GETINTS(a,b) {char s[34];int *ap=a;REP(i,b){GETWORD(s);*ap++=atoi(s);}}
static int GETLINEINT(void) {char s[34];GETLINE(s);return atoi(s);}
static int GETWORDINT(void) {char s[34];GETWORD(s);return atoi(s);}
#define SWAP(type,a,b) do{type _c;_c=a;a=b;b=_c;}while(0)

static int max(int a,int b){if(a>b){return a;}return b;}
static int min(int a,int b){if(a<b){return a;}return b;}
// for readaility
typedef	long long	lolong;
const int	INF = 1e9;
const int	MOD = 1e9+7;
const lolong	LINF = 1e18;
#define PI	  ((double)3.141592653589793238462643383279)
#define	YES(a)	printf("%s",((a)?"YES":"NO"))
#define	Yes(a)	printf("%s",((a)?"Yes":"No"))
#define OK(a)	printf("%s",((a)?"OK":"NG"))
#define Ok(a)	printf("%s",((a)?"Ok":"Ng"))
#define	POSSIBLE(a)		printf("%s",((a)?"POSSIBLE":"IMPOSSIBLE"))
#define	Possible(a)		printf("%s",((a)?"Possible":"Impossible"))
#define SWAP(type,a,b) do{type _c;_c=a;a=b;b=_c;}while(0)
#define REP(a,b) for(int a=0;a<(int)(b);++a)
#define REP1(a,b) for(int a=1;a<=(b);++a)
#define FLOOP(a,b) for(a=0;a<(b);++a)
#define FLOOP1(a,b) for(a=1;a<=(b);++a)
#define	ABS(c)	 ((c)<0?(-(c)):(c))
#define LSB(i) ((i) & -(i))
#define INPBUF (250+2)

#define	data_s	int
// ***********************
// ***********************
static int cmpint_asc(const void *a,const void *b){if(*(int *)a>*(int *)b){return 1;}if(*(int *)a==*(int *)b){return 0;}return -1;}
static int cmpint_desc(const void *a,const void *b){if(*(int *)a<*(int *)b){return 1;}if(*(int *)a==*(int *)b){return 0;}return -1;}
static int cmpchar_asc(const void *a,const void *b){if(*(char *)a>*(char *)b){return 1;}if(*(char *)a==*(char *)b){return 0;}return -1;}
static int cmpchar_desc(const void *a,const void *b){if(*(char *)a<*(char *)b){return 1;}if(*(char *)a==*(char *)b){return 0;}return -1;}
static int mystr_len(char *str){int i=0;do{if(str[i]=='\0')break;i++;if(i>9999)break;}while(1);return i;}
static int countchar(char str[],char c,int limit ) {int	cnt = 0;for(int i=0;i<limit;i++) if( str[i] == c )cnt++;return cnt;}
// ***********************
// ***********************
// ***********************
// ***********************
// ***********************
// ***********************
// 外部変数
// ***********************
// ***********************
// ***********************
void cpycpy( char *A2, char *A ) {
	int		len;

	len = strlen( A );
	A2[11] = '\0';
	for(int i = 10;i >= 0 ; --i ) {
		if( len ) {
			len--;
			A2[i] = A[len];
		} else {
			A2[i] = '0';
		}
	}
}
int	strcmpcmp( char *A1, char *A2 ) {
	char *p1 = A1;
	char *p2 = A2;

	while( *p1 != '\0' ) {
		if( ( *p1 == '4' )&&( *p2 == '7' ) ) {
			return 1;
		} else if( ( *p1 == '7' )&&( *p2 == '4' )) {
			return -1;
		} else {
			if( *p1 != *p2 ) {
				return *p1 - *p2;
			}
		}
		p1++;	p2++;
	}
	return 0;
}
// ***********************
int main() {
	char	A[16];
	char	B[16];
	char	A2[16];
	char	B2[16];


	GETWORD(A);
	GETWORD(B);

	cpycpy( A2, A );
	cpycpy( B2, B );

	TRACE("A2[%s]\nB2[%s]\n", A2, B2);
	if( strcmpcmp( A2 , B2 ) > 0 ) {
		printf("%s\n", A);
	} else {
		printf("%s\n", B);
	}
	return 0;
}