Get the sequence chars from given text

Program:
public class Series {
    public static void main(String arg[]){
        String str = "yuwetabcdefgrqwyu";
        System.out.println(str);

        char ch[]= str.toCharArray();
        char result[] = new char[20];
        int c=0, f=0;
        result[0]=ch[0];
        if(ch[1] == result[0]+1)
            c++;
        for(int i=1;i<ch.length-1;i++){
            if((ch[i] == ch[i-1]+1) || (ch[i] == ch[i+1]-1)){
                result[c++] = ch[i];
            }
        }
        if(ch[ch.length-1] == result[c-1]+1)
            result[c++] = ch[ch.length-1];
        System.out.println(String.valueOf(result));
    }  

}

Input:
yuwetabcdefgrqwyu

Output:
abcdefg