Untitled

#include <bits/stdc++.h>

using namespace std;
/***********************************************/
/* Dear online judge:
 * I've read the problem, and tried to solve it.
 * Even if you don't accept my solution, you should respect my effort.
 * I hope my code compiles and gets accepted.
 *  ___  __     _______    _______      
 * |\  \|\  \  |\  ___ \  |\  ___ \     
 * \ \  \/  /|_\ \   __/| \ \   __/|    
 *  \ \   ___  \\ \  \_|/__\ \  \_|/__  
 *   \ \  \\ \  \\ \  \_|\ \\ \  \_|\ \ 
 *    \ \__\\ \__\\ \_______\\ \_______\
 *     \|__| \|__| \|_______| \|_______|
 */
const long long mod = 1000000007;
#define ll long long
#undef ll

const int mxN = 2510;

int get(int x){
	for(int i = 0;i*(i-1)/2 <= x;i++)
		if(i * (i - 1) / 2 == x)return i;
	return -1;
}

int main(int argc, char** argv) {
#ifdef ONLINE_JUDGE
	ios_base::sync_with_stdio(0);
	cin.tie(0);
#endif

	int a[4] = {};
	for(int i = 0; i < 4; i++)cin >> a[i];
	if(*max_element(a,a+4) == 0){
		cout << 1 << '\n';
		return 0;
	}
	
	int zeros = get(a[0]);
	int ones = get(a[3]);
	if(a[1]||a[2]){
		zeros = max(zeros,1);
		ones = max(ones,1);
	}
	if(zeros * (zeros - 1) / 2 != a[0] || ones * (ones - 1) / 2 != a[3]){
		cout << "impossible\n";
		return 0;
	}
	
	string ans = "";
	
	while(zeros || ones){
		if(zeros > 0 && a[1] >= ones)
			a[1] -= ones, zeros--, ans.push_back('0');
		else if(ones > 0 && a[2] >= zeros)
			a[2] -= zeros, ones--,	ans.push_back('1');
		else{
			cout << "impossible\n";	return 0;
		}
		
		
	}
	if(a[1] || a[2]){
			cout << "impossible\n";	return 0;
		}
		
		cout << ans << '\n';
	

	return 0;
}