不要说是我炒的

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

long long a[200005];

int main() {
int n;
cin >> n;
for (int i = 0; i < n; ++i) {
cin >> a[i];
}
long long triangles = 0;
long long b = a[0] / 3;
a[0] %= 3;
long long les = a[0];
for (int i = 1; i < n; ++i) {
long long num = min(les, a[i] / 2);
les -= num;
a[i] -= num * 2;
b += num;
b += a[i] / 3;
a[i] %= 3;
les += a[i];
}
cout << b << endl;

return 0;

}