#include<iostream>
#include<cstring>
using namespace std;
char a[3000] , b[3000];
int n ,len;
bool pd()
{
	for(int i = 0;i < len;i++ )
		if(a[i] != a[len - i - 1]) return false;
	return true;
}
void add()
{
	for(int i = 0;i < len;i++)
		b[len - i - 1] = a[i];
	len+=2;
	for(int i = 0;i < len;i++)
	{
		a[i] += b[i];
		if (a[i]>=n) a[i+1]++,a[i]-=n;
	}
	for(;!a[len];) len--;
}
int main()
{
	scanf("%d%s",&n,a);
	len = strlen(a);
	for(int i = 0;i < len;i++)
	{
		if(a[i] >= '0'&&a[i] <= '9') a[i] -= '0';
		else a[i] =a[i] - 'A' + 10;
	}
	int huan = 0;
	while(!pd())
	{
		huan ++;
		if(huan > 30)
		{
			break;
		}
		
		add();
	}
	if (huan<=30) printf("STEP=%d\n",huan);
	else puts("Impossible!");
	return 0;
}
 

//照第一遍题解写的