k, n, s, p = map(int, input().split())
sheets_per_person = (n + s - 1) // s
sheets = k * sheets_per_person
print((sheets + p - 1) // p)#include<iostream>
using namespace std;
long long k, n, s, p;
int main()
{
cin >> k >> n >> s >> p;
cout << ((n + s - 1) / s * k + p - 1) / p ;
return 0;
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