#include<stdio.h>
int main(int argc,char** argc){
int num;
int digit[8]={0};
int max,min;
if(scanf("%d",&num)!1||num<0||num>100000000){
printf("error");
return 0;
}
int temp=num;
while(temp>0){
digit[count]=temp%10;
count=count+1;
temp=temp/10;
}
max=min=digit[0];
for(int i=1;i<count;i++){
if(digit[i]>max){
max=digit[i];
}
if(digit[i]<min){
min=digit[i];
}
int product=min*max;
printf("%d",product);
return 0;
}
}