#include <iostream>
using namespace std;
int main() {
int w, h, n, a, b;
cin >> w >> h >> n >> a >> b;
int page = (w / a) * (h / b);
if (page == 0) {
cout << -1;
} else {
int pages = n / page;
if (n % page != 0)
pages++;
cout << pages;
}
return 0;
}
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