text: /*****
   * 
   * 用字符串拼最少的回文数
   * 
   * 2019.06.19
   * 
   */
  
  
  function findminNumofStr(str){
      let minNum = 0;
      let arr = str.split('');
      // 转换成数组后，进行归并迭代
      minNum = arr.reduce((tempSet,ele)=> {
          return tempSet.delete(ele)? tempSet:tempSet.add(ele);
      },new Set()).size;
      if(minNum === 0){
          minNum = 1;
      }
      return minNum;
  }
  
  
  
  var initPre = readline().split(" ");
  var linstr = initPre[0];
  print(findminNumofStr(linstr))