codeforces Gym 100338E Numbers

#include<bits/stdc++.h>
using namespace std;
typedef unsigned long long ull;
const int maxbit = 19;
ull base[maxbit], n, k;

void preDeal()
{
    base[0] = 1;
    for(int i = 1; i < maxbit; i++){
        base[i] = 10*base[i-1];
    }
}


void ull2str(ull x,string& s)
{
    int st[maxbit],top = 0;
    while(x){
        st[top++] = x%10+‘0‘;
        x /= 10;
    }
    reverse(st,st+top);
    s.assign(st,st+top);
}

void work()
{
    priority_queue<string,vector<string>,greater<string> > q;
    int sz = maxbit-1;
    while(base[sz]>n) sz--;
    string str;
    for(int i = 0; i <= sz; i++){
        ull cur = base[i];
        ull r = cur%k;
        if(r != 0){
            cur += k-r;
        }
        if(cur <= n){
            ull2str(cur,str);
            q.push(str);
        }
    }
    printf("%s\n",q.top().c_str());
}

int main()
{
    freopen("numbers.in","r",stdin);
    freopen("numbers.out","w",stdout);
    preDeal();
    while(scanf("%I64u%I64u",&n,&k),n){
        work();
    }
    return 0;
}