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

#define long long long
#define f1(i,n) for (int i=1; i<=n; i++)
#define f0(i,n) for (int i=0; i<n; i++)
typedef pair<int, int> ii;
typedef pair<ii, ii> quad;
#define X first
#define Y second

quad rect(int x, int y, int u, int v)
    { return quad(ii(x, y), ii(u, v)); }

#define N 2003
int n;
char a[N], F[N];
bool Visited[N][N];

void bfs(){
    queue<quad> qu;
    qu.push(rect(1, n, '\0', 0));
    while (qu.size()) {
        quad Top=qu.front(); qu.pop();
        int x=Top.X.X, y=Top.X.Y;
        int u=Top.Y.X, v=Top.Y.Y;
        if (F[v]!=u || x>y) continue;
        if (Visited[x][y]++) continue;

        F[v+1] = min(F[v+1], min(a[x], a[y]));
        qu.push(rect(x+1, y, a[x], v+1));
        qu.push(rect(x, y-1, a[y], v+1));
    }
}

main(){
    scanf("%d", &n);
    f1(i,n) {
        scanf(" %c", &a[i]);
        F[i]='z';
    }
    bfs();
    f1(i,n) {
        printf("%c", F[i]);
        if (i%80==0) printf("\n");
    }
}