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#include<iostream>
#include<cmath>
using namespace std;
int main(){
unsigned long long sum=0;
int p;
cin>>p;
string cnt;
cin>>cnt;
int len=cnt.size();
for(int i=len-1;i>=0;i--){
if(cnt[i]>='A' and cnt[i]<='F'){
sum+=(cnt[i]-'A'+10)*pow(p,len-i-1);
}
else{
sum+=(cnt[i]-'0')*pow(p,len-i-1);
}
}
cout<<sum;
return 0;
}