#include <cstdio>
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <string.h>
#include <queue>
#include <map>
#include <set>
#include <deque>
#include <cmath>
#include <sstream>
#include <stack>
#include <cassert>

#define pb push_back
#define mp make_pair
#define sqr(x) (x)*(x)

using namespace std;

const int MAXN = 200500;

int k,n;
char s[MAXN];
int r;

int chislo(char x)
{
    if ( isdigit(x) )
        return (int)(x-'0');
        else return 10+(int)(x-'A');
}

int main()
{
    freopen("code.in", "r", stdin);
    freopen("code.out", "w", stdout);
    scanf("%d %d%*c", &k, &n);
    scanf("%s", s);
    k--;
    r=-1;
    int l =0;
    //while ( l<n && s[l] == '0')  l++;
    for (int i=n-1; i>=l; i--)
    {
        int t = chislo(s[i]);
        if ( t<k)
        {
            if ( r != -1)
            {
                t++;
                sort(s+i+1, s+n);
                for (int j=i+1; j<n; j++)
                    if ( s[j] != '0' )
                    {
                        r=j;
                        break;
                    }
                int t2 = chislo(s[r]);
                t2--;
                if ( t < 10)
                    s[i] = (char)('0'+t);
                    else
                    {
                        t-=10;
                        s[i] = (char)('A'+t);
                    }
                if ( t2 < 10)
                    s[r] = (char)('0'+t2);
                    else
                    {
                        t2-=10;
                        s[r] = (char)('A'+t2);
                    }
                sort(s+i+1, s+n);
                printf("%s", s);
                return 0;
            }
        }
        if ( t > 0)
            r = i;
    }
    printf("Impossible");
}