C :

#include <stdio.h>
void main() {
    void complement(char p[], char ret[]);
    char p[20], ret[20];
    scanf("%s", p);
    complement(p, ret);
    printf("%s\n", ret);
}
void complement(char p[], char ret[]) {
    int i, add;
    if (p[0] == '1') {
        ret[0] = '1';
        for (i = 1;i < 16;i++)
            if (p[i] == '1')
                ret[i] = '0';
            else
                ret[i] = '1';
        i = 15;
        add = 1;
        while (add > 0) {
            add = (ret[i] - '0') + add;
            ret[i] = '0' + (add & 1);
            i--;
            add >>= 1;
        }
        ret[16] = '\0';
    } else {
        strcpy(ret, p);
    }
}

C++ :

#include<iostream>
#include<cstring>
using namespace std;
int main()
{
  char s[20];
  cin>>s;
  for(int i=1;i<strlen(s);i++)
    if(s[i]=='0')s[i]='1';
    else s[i]='0';
    
  for(int i=strlen(s)-1;i>=1;i--)
    if(s[i]=='0'){s[i]='1';break;}
  else s[i]='0';
  cout<<s<<endl;
  return 0;
}

Pascal :

Program TK1322;
var s:string; l,i,j:longint;

Begin 
	readln(s);
	if s[1]='0' then begin 
		writeln(s); exit;
	end; l:=length(s)-1;
	for i:=1 to l do s[i]:=s[i+1];
	s[l+1]:=' '; write('1');
	for i:=l downto 1 do if s[i]='1' then begin 
		s[i]:='0'; 
		for j:=i+1 to l do s[i]:='1';
	end; 
	for i:=1 to l do if s[i]='0' then s[i]:='1'
		else if s[i]='1' then s[i]:='0';
	writeln(s);
End.	

Java :

import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner cin=new Scanner(System.in);
		String s=cin.nextLine();
		cin.close();
		if(s.substring(0,1)=="0")
			System.out.println(s);
		else{
		int a=Integer.parseInt(s,2);
		int sum=1;
		while(sum<a)
			sum*=2;
		sum/=2;
		a-=sum;
		a=~a;
		a+=sum;
		a++;
		System.out.println("1"+Integer.toBinaryString(a));
		}
	}
}