Cod sursă (job #710028)

#include <fstream>
#define L 5e6 + 5
#define FAIL L + 1
using namespace std;

ifstream cin("scv.in" );
ofstream cout("scv.out" );

long long upd, timpscv, total, x, t, currentSCV, m, nrscv;
long long tmin;
int state;


long long fi();

void fct() {
  if (t > L) {
    state = 6;
  }
  tmin = min(tmin, fi());
  state = 2;
}

void done() {
  if (upd <= m) {
    m -= upd;
    state = 5;
    return;
  }

  long long deltaTime = (upd - m + currentSCV * total - 1)
/ (currentSCV * total);
  t += deltaTime;
  m += deltaTime * currentSCV * total;
  if (t > L) {
    state = 6;
  } else {
    m -= upd;
    state = 5;
  }
}

long long fi() {
  if (x <= m) {
    return t;
  }

  long long deltaTime = (x - m + currentSCV * total - 1)/(currentSCV * total);
  if (t + deltaTime > L) {
    return L;
  } else {
    return t + deltaTime;
  }
}

void scv() {
  m += currentSCV * total * timpscv;
  t += timpscv;
  if (t > L) {
    state = 6;
  } else {
    currentSCV++;
    state = 1;
  }
}

int main(){
  cin >> upd >> timpscv >> total >> x;

  t = m = 0;
  currentSCV = 1;
  state = 1;
  tmin = L;

  int iter = L;
  while (t < tmin && state != 6 && iter) {
    switch (state) {
      case 1:
        fct();
        break;
      case 2:
        done();
        break;
      case 5:
        scv();
        break;
    }
    iter--;
  }

  cout << tmin << "\n";
  return 0;
}