Cod sursă (job #765715)

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

bool f(int &mid, int &c, int &t, int &m, int &x) {
    int k = (c/m) - (c % m == 0 ? 1 : 0), scvs = 1, countdown = 0;
    k *= m;
    for(int i = (c / m + (c % m == 0 ? 0 : 1)); i <= mid; i++) {
        if(countdown) --countdown;
        k += (scvs*m);
        if(k >= c && countdown == 0) {
            int rem_days = mid-i+1-t;
            if(rem_days * m > c) {
                k -= c;
                k -= (m * t);
                scvs++;
                countdown = t;
            }
        }
        if(k >= x) return true;
    }
    return false;
}

int main()
{
    freopen("scv.in", "r", stdin);
    freopen("scv.out", "w", stdout);
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int C, T, M, X;
    cin >> C >> T >> M >> X;
    int l = 1, r = (X/M+1);
    while(l <= r) {
        int mid = (l+r)/2;
        if(f(mid, C, T, M, X)) {
            r = mid-1;
        }
        else l = mid+1;
    }
    cout << l;
    return 0;
}