#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, d, m, l;
  scanf("%d%d%d%d", &n, &d, &m, &l);
  long long a, b;
  for (int i = 1; i <= n; i++) {
    a = 1ll * (i - 1) * m + l, b = 1ll * i * m - 1;
    if (a / d != b / d) break;
  }
  printf("%lld\n", a - a % d + d);
  return 0;
}
