#include<bits/stdc++.h>
using namespace std;
#define int unsigned long long
int n,ans;
string m,s;
bool asn(){
	string s1=s;
	reverse(s.begin(),s.end());
	if (s1!=s){
		return false;
	}
	return true;
}
signed main(){
	cin>>n>>m;
	for(int i=0;i<m.size();i++){
		if (m[i]>='A'&&m[i]<='Z'){
			m[i]='9'+m[i]-'A'+1;
		}
	}
	s=m;
	while(!asn()){
		string s1=s;
		reverse(s.begin(),s.end());
		string s2;
		int r=0;
		for(int i=0;i<s.size();i++){
			int x=s[i]-'0';
			int y=s1[i]-'0';
			char z=(x+y+r)%n+'0';
			r=(x+y+r)/n;
			s2=z+s2;
		}
		if (r){
			char x=r+'0';
			s2=x+s2;
		}
		s=s2;
		ans++;
		if (ans>30){
		    cout<<"Impossible!";
		    return 0;
		}
	}
	cout<<"STEP="<<ans;
	return 0;
}