import std.stdio,
       std.string,
       std.conv,
       std.algorithm;

void main() {
  long[] buf = readln.chomp.split.to!(long[]);
  long q = buf[0],
      h = buf[1],
      s = buf[2],
      d = buf[3];
  long N = readln.chomp.to!(long);

  long min_cost_per_1L = min(q * 4, h * 2, s);
  long min_cost_per_2L = min(q * 8, h * 4, s * 2, d);

  writeln(
      min((N / 2 * min_cost_per_2L + N % 2 * min_cost_per_1L), (N * min_cost_per_1L))
      );
}
