#include <stdio.h>
int main() {
int n;
scanf("%d ",&n);
int max=-100;
int b=n;
while(b>0){
int t=b-(b/10);
b=b/10;
if(t>max){
max=t;
}
}
int mini=100;
int v=n;
while(v>0){
int k=v-(v/10);
v=v/10;
if(k<mini){
mini=k;
}
}
printf("%d\n",mini*max);
return 0;
}