#include <iostream>
#include <stdio.h>
#include <vector>
using namespace std;

int n;
char str[100011];
int RightDif[100011];
int LeftDif[100011];
vector<char> ans;

int main()
{
    freopen("code.in","r",stdin);
    freopen("code.out","w",stdout);

    int i,j;
    int L,R;
    char T1,T2;
    int D1,D2;

    scanf("%d",&n);
    scanf("%s",str+1);

    RightDif[n]=-1;
    for (i=n-1;i>=1;i--)
    {
        if (str[i]==str[i+1])
        RightDif[i]=RightDif[i+1];
        else
        RightDif[i]=i+1;
    }

    LeftDif[1]=-1;
    for (i=2;i<=n;i++)
    {
        if (str[i]==str[i-1])
        LeftDif[i]=LeftDif[i-1];
        else
        LeftDif[i]=i-1;
    }

    L=1;
    R=n;

    while(L<=R)
    {
        if (str[L]<str[R])
        {
            ans.push_back(str[L]);
            L++;
        }
        else if (str[L]>str[R])
        {
            ans.push_back(str[R]);
            R--;
        }
        else
        {
            for (i=L,j=R;i<=R && j>=L;i++,j--)
            {
                T1=str[i];
                T2=str[j];

                if (T1<T2)
                {
                    ans.push_back(str[L]);
                    L++;
                    break;
                }
                else if (T1>T2)
                {
                    ans.push_back(str[R]);
                    R--;
                    break;
                }
            }

            if (i==R+1)
            {
                ans.push_back(str[L]);
                L++;
            }
        }
    }

    for (i=0;i<ans.size();i++)
    {
        printf("%c",ans[i]);
    }
    printf("\n");

    return 0;
}