Intial of string in java

import java.io.*;
public class initial_str
{
public static void main()throws IOException
{
InputStreamReader isr=new InputStreamReader(System.in);
BufferedReader br=new BufferedReader(isr);
char ch;
String s1,res=" ";
int i,j,c=0;
System.out.println("Enter the string ");
s1=br.readLine();
i=s1.length();
res=res+s1.charAt(0)+'.';
for(j=1;j<i;j++)
{
ch=s1.charAt(j);
if(ch==' ')
res=res+s1.charAt(j+1)+'.';
}
System.out.println(res);
}
}