#include<bits/stdc++.h>
using namespace std;
int main(){
	int x,ans=0;
	string s;
	cin>>x>>s;
	reverse(s.begin(),s.end());
	for(char i:s)ans=ans*x+(i>='A'&&i<='Z'?10+i-'A':i-'0');
	cout<<ans;
	return 0;
}