#include <bits/stdc++.h>
using namespace std;

typedef unsigned long long ull;

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

	char c;
	deque<tuple<int, int, int>> blocks;
	deque<tuple<int, int>> frees;
	int i = 0, n = 0;
	bool rfree = false;
	while (cin >> c) {
		c -= '0';
		if (rfree) {
			if (c > 0) {
				frees.push_back({n, c});
			}
		} else {
			blocks.push_back({i++, n, c});
		}
		rfree = !rfree;
		n += c;
	}

	while (frees.size() > 0) {
		auto &[bi, bx, bn] = blocks.back();
		auto &[fx, fn] = frees[0];
		if (fx > bx) {
			break;
		}
		int nmoved = min(fn, bn);
		bn -= nmoved;
		fn -= nmoved;
		blocks.push_front({bi, fx, nmoved});
		if (fn == 0) {
			frees.pop_front();
		} else {
			fx += nmoved;
		}
		if (bn == 0) {
			blocks.pop_back();
		}
	}

	ull sum = 0;
	for (auto &[bi, bx, bn] : blocks) {
		sum += (ull)bi * (bn * bx + bn * (bn - 1) / 2);
	}
	cout << sum << '\n';
}