702D - Road to Post Office - CodeForces Solution

#include<bits/stdc++.h>
#define int long long 


using namespace std;

int a, b, d, k, t;

int calc(int x)
{
		return a * x + (x / k - (x % k == 0 && x != 0)) * t + (d - x) * b;
}

signed main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);
	cin >> d >> k >> a >> b >> t;
	if (a > b)
	{
		cout << d * b;
		return 0;
	}

	int ans = LLONG_MAX, l = 0, r = d;

	for (int i = 0; i <= 1e6; ++i)
		ans = min(ans, calc(min(i, d)));

	for (int i = d - 1e6; i <= d; ++i)
		ans = min(ans, calc(max(i, 0ll)));


	cout << ans;

    cerr << "\nTime elapsed: " << 1000.0 * clock() / CLOCKS_PER_SEC << " ms.\n";
}