/*
	Autor: Slobodan Mitrovic
*/
#include <iostream>
#include <cstdio>
#include <fstream>
#include <vector>
#include <cmath>
#include <time.h>
#define ffor(_a,_f,_t) for(int _a=(_f),__t=(_t);_a<__t;_a++)
#define all(_v) (_v).begin() , (_v).end()
#define sz size()
#define pb push_back
#define SET(__set, val) memset(__set, val, sizeof(__set))
#define FOR(__i, __n) ffor (__i, 0, __n)

using namespace std;

const int MAXN = 5000, MOD = 1000000007;

char str[MAXN + 10];

int fastMod(int val){
//  return val % MOD;
  if (val > MOD)
    return val - MOD;
  return val;
}


int fastestDP[MAXN + 1][MAXN + 1];

int fastestSolution(int n){
  SET(fastestDP, 0);
  int *cur;
  for (int i = n - 1; i > -1; i--){
    fastestDP[i][i] = 1;
    for (int j = i + 1; j < n; j++){
      cur = &fastestDP[i][j];
      *cur = fastMod(fastestDP[i][j - 1] + fastestDP[i + 1][j]); 
      *cur = fastMod((*cur) - fastestDP[i + 1][j - 1] + MOD);
      if (str[i] == str[j])
        *cur = fastMod((*cur) + 1 + fastestDP[i + 1][j - 1]);
    }
  }
  return fastMod(fastestDP[0][n - 1]);
}

int main(){
  FILE *fin;
  FILE *fout;


  fin = fopen("progsice.in", "r");
  fout = fopen("progsice.sol", "w");

  int n;
  fscanf(fin, "%d\n", &n);
  FOR (i, n)
    fscanf(fin, "%c", &str[i]);
    
  fprintf(fout, "%d\n", fastestSolution(n));
  fclose(fin);
  fclose(fout);
  return 0;
}