LEXDIV C++

#include <bits/stdc++.h>
using namespace std;

int a,b,k;
string minn,si;

string so_thanh_xau(int x)
{
    string s="";
    int k;
    while(x>0)
    {
        k=x%10;
        x=x/10;
        s=char(k+48)+s;
    }
    return s;
}

void giai()
{
    minn="a";
    for(int i=a;i<=b;i++)
    {
        if(i%k==0)
        {
            si = so_thanh_xau(i);
            if(si<minn) minn=si;
        }
    }
    cout << minn;
}
int main()
{
    freopen("lexdiv.inp","r",stdin);
    freopen("lexdiv.out","w",stdout);
    cin >> a >> b >> k;
    giai();
}