#include <bits/stdc++.h>
using namespace std;
const int MAXN = 410;
struct bign {
  int len;
  int s[MAXN];
  bign() {
    memset(s, 0, sizeof(s));
    len = 1;
  }
  bign(const char *num) { *this = num; }
  bign(int num) { *this = num; }
  bign operator=(const int num) {
    char s[MAXN];
    sprintf(s, "%d", num);
    *this = s;
    return *this;
  }
  bign operator=(const char *num) {
    for (int i = 0; num[i] == '0'; num++)
      ;
    len = strlen(num);
    for (int i = 0; i < len; i++) {
      s[i] = num[len - i - 1] - '0';
    }
    return *this;
  }
  void clean() {
    while (len > 1 && !s[len - 1]) len--;
  }
  string str() const {
    string res = "";
    for (int i = 0; i < len; i++) {
      res = char(s[i] + '0') + res;
    }
    return res;
  }
  bool operator<(const bign &b) {
    if (len != b.len) return len < b.len;
    for (int i = len - 1; i >= 0; i--) {
      if (s[i] != b.s[i]) return s[i] < b.s[i];
    }
    return false;
  }
  bign operator+(const bign &b) const {
    bign c;
    c.len = 0;
    for (int i = 0, g = 0; g || i < max(len, b.len); i++) {
      int x = g;
      if (i < len) x += s[i];
      if (i < b.len) x += b.s[i];
      c.s[c.len++] = x % 10;
      g = x / 10;
    }
    return c;
  }
  bign operator*(const bign &b) {
    bign c;
    c.len = len + b.len;
    for (int i = 0; i < len; i++) {
      for (int j = 0; j < b.len; j++) {
        c.s[i + j] += s[i] * b.s[j];
      }
    }
    for (int i = 0; i < c.len; i++) {
      c.s[i + 1] += c.s[i] / 10;
      c.s[i] %= 10;
    }
    c.clean();
    return c;
  }
  bign operator-(const bign &b) {
    bign c;
    c.len = 0;
    for (int i = 0, g = 0; i < len; i++) {
      int x = s[i] - g;
      if (i < b.len) x -= b.s[i];
      if (x >= 0)
        g = 0;
      else {
        g = 1;
        x += 10;
      }
      c.s[c.len++] = x;
    }
    c.clean();
    return c;
  }
  bign operator/(const bign &b) {
    bign c, f = 0;
    for (int i = len - 1; i >= 0; i--) {
      f = f * 10;
      f.s[0] = s[i];
      while (!(f < b)) {
        f = f - b;
        c.s[i]++;
      }
    }
    c.len = len;
    c.clean();
    return c;
  }
  bign operator%(const bign &b) {
    bign r = *this / b;
    r = *this - r * b;
    return r;
  }
};
istream &operator>>(istream &in, bign &x) {
  string s;
  in >> s;
  x = s.c_str();
  return in;
}
ostream &operator<<(ostream &out, const bign &x) {
  out << x.str();
  return out;
}
int main() {
  bign d, k, a, b, t;
  cin >> d >> k >> a >> b >> t;
  bign rr = d / k;
  bign yi(1);
  bign result;
  bign aaa = d * b;
  bign bbb = ((rr) * (t) + rr * a * k + (d % k) * a);
  bign ddd = ((rr - 1) * t + rr * a * k + (d % k) * b);
  bign ccc = (b * (d - k) + a * k);
  if (aaa < bbb)
    result = aaa;
  else
    result = bbb;
  if (ccc < result) result = ccc;
  if (ddd < result) result = ddd;
  cout << result << endl;
}
