Codeforce 672B. Different is Good

A wise man told Kerem "Different is good" once, so Kerem wants all things in his life to be different. 

Kerem recently got a string s consisting of lowercase English letters. Since Kerem likes it when things are different, he wants all substrings of his string s to be distinct. Substring is a string formed by some number of consecutive characters of the string. For example, string "aba" has substrings "" (empty substring), "a", "b", "a", "ab", "ba", "aba".

If string s has at least two equal substrings then Kerem will change characters at some positions to some other lowercase English letters. Changing characters is a very tiring job, so Kerem want to perform as few changes as possible.

Your task is to find the minimum number of changes needed to make all the substrings of the given string distinct, or determine that it is impossible.

Input

The first line of the input contains an integer n (1 ≤ n ≤ 100 000) — the length of the string s.

The second line contains the string s of length n consisting of only lowercase English letters.

Output

If it's impossible to change the string s such that all its substring are distinct print -1. Otherwise print the minimum required number of changes.

初看吓了一跳还以为这么多子串怎么办，不过仔细一想不就是保证每一位的字母都不一样吗。当n>26时字母不够用当然-1

否则就是统计那些重复的字符数即可

#include <cstdio>
#include <cctype>
#include <stdlib.h>
#include <iostream>
#include <cmath>
#include <iomanip>
#include <cstring>
#include <algorithm>
#include <string>
#include <vector>
#include <map>

using namespace std;
typedef long long LL;
int n;
char s[100005];
int appear[26] = {0};
int main()
{
  // freopen("test.in","r",stdin);
  cin >> n;
  cin >> s;
  int len = strlen(s);
  if (len > 26){
    cout << -1; return 0;
  }
  for (int i=0;i<len;i++){
    appear[s[i] - 'a'] ++;
    // cout << s[i];
  }
  int total = 0 ;
  for (int i=0;i<26;i++){
    if (appear[i] > 1){
      total += appear[i] - 1;
    }
  }
  cout << total;
  return 0;
}