#include <iostream>
using namespace std;
int x=49,n,a,b,d;
char c;
int main(){
cin>>n>>a>>b>>d;
if(a>0){
if(a==1){
c = x+'0';
cout<<char(toupper(c));
}else if(a>1){
for(int i=0;i<=a;i++){
x=x+i;
c = x+'0';
cout<<char(toupper(c));
}
}
if(b==1){
x++;
c = x+'0';
cout<<char(tolower(c));
}else if(b>1){
for(int i=1;i<=b;i++){
x=x+i;
c = x+'0';
cout<<char(tolower(c));
}
}
x=48;
if(d==1){
c = x+'0';
cout<<c;
}else if(d>1){
for(int i=0;i<=d;i++){
x=x+1;
c = x+'0';
cout<<c;
}
}
}
return 0;
}
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