#include<bits/stdc++.h>
using namespace std;
long long n,sum,k=0;
string s;
int main()
{
cin>>n;
cin>>s;
for(int i=s.size()-1;i>=0;i--)
{
if(s[i]>='A' and s[i]<='Z') sum+=(s[i]-55)*pow(n,k);
else sum+=(s[i]-'0')pow(n,k);
k++;
}
cout<<sum;
return 0;
}
/
*/
