#include <cstdio>
#include <cstdlib>

int main(){
  int n;
  scanf("%d",&n);
  char s[n+2];
  scanf("%s",s);
  if (n==2){
    printf("%d\n",s[0]==s[1]?2:1);
    return 0;
  }
  int m[20][n+1];
  for (int i=0;i<20;i++)
    m[i][0]  = 0;
  for (int a=0;a<n;++a){
    for (int i=0;i<20;++i){
      m[i][a+1] = m[i][a];
    }
    m[s[a]-'a'][a+1] = m[s[a]-'a'][a] + 1;
  }
  int from=1;
  int to=n;
  int mx = 1;
  while (from<to){
    int a=(from+to+1)/2;
    //printf("vo while from %d to %d\n", from, to);
    char found=0;
    int np;
    for (int b=0;(b + a) < n;b++) {
      np = 0;
      for (int c=0; c < 20; c++) {
        if ((m[c][b + a +1] - m[c][b]) % 2)
          ++np;
      }
      if (np<2){
        found=1;
	mx = a;
     //   printf("mx %d\n", mx);
        break;
      }
    }
 //   printf("mx %d np %d\n", mx, np);
  int p = 0;
    if (found){
   //   printf("from\n");
      from = a;
    } else {
     // printf("to\n");
      to = a - 1;
    }
  }
  printf("%d\n",mx+1);
  return 0;
}