#include <iostream>
#include <cstring>
#include <vector>
#include <cmath>
#include <algorithm>
#include <map>
using namespace std;

long long SecvBiti(char s[]) {
	int nr0 = 0, nr1 = 0, ans = 0;
	int t[2000001];
	for (int i = 0; i < strlen(s); i++) {
		nr0 += (s[i] == '0');
		nr1 += (s[i] == '1');
		t[i] = nr1 - nr0;
	}
	return ans;
}

int main() {

	cout << SecvBiti("1001");

	return 0;
}