#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;
    int sum = 0;
    int pre = 0;
    while (cin >> n) {
        if (n == 0) break;
        if (n == 1) {
            sum++;
            pre = 0;
        }
        if (n == 2) {
            pre += 2;
            sum += pre;
        }
    }
    cout << sum << endl;
    return 0;
}