100%AC

#include<bits/stdc++.h>
using namespace std;
int a[2005],b[2005];
string ans="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
void f(string s,int c[]){
    int len=s.size();
    for(int i=1;i<=len;i++){
        if(s[len-i]>='0'&&s[len-i]<='9')c[i]=s[len-i]-'0';
        else c[i]=s[len-i]-'A'+10;
    }
}
int main(){
    int k;
    string s,ss;
    cin>>k>>s>>ss;
    f(s,a);
    f(ss,b);
    int len=max(s.size(),ss.size());
    for(int i=1;i<=len;i++){
        a[i]+=b[i];
        if(a[i]>=k)a[i+1]+=a[i]/k,a[i]%=k;
    }
    if(a[len+1]>0)len++;
    for(int i=len;i>=1;i--){
        cout<<ans[a[i]];
    }
    return 0;
}

c++98 so easy!******简单死了！