题解100%AC

#include <bits/stdc++.h>
using namespace std;
char charnum(int x){
    if(x<10) return x+'0';
    else return x-10+'A';
}
int main(){
    long long a,b,r;
    cin>>a>>b>>r;
    string a1="",b1="";
    while(a){
        a1=charnum(a%r)+a1;
        a/=r;
    }
    while(b){
        b1=charnum(b%r)+b1;
        b/=r;
    }
    if(a1<b1)cout<<b1;
    else cout<<a1;
}