import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.Arrays; import java.util.NoSuchElementException; import java.util.Scanner; public class Main { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); //FastScanner scanner=new FastScanner(); PrintWriter out = new PrintWriter(System.out); int gx=scanner.nextInt(); int gy=scanner.nextInt(); int n=scanner.nextInt(); int f=scanner.nextInt(); final int INF=1000000; int[][] d=new int[gx+1][gy+1]; for(int i=0; i<=gx; i++) Arrays.fill(d[i], INF); d[0][0]=0; int[] x=new int[n]; int[] y=new int[n]; int[] c=new int[n]; for(int i=0; i=0; i--) { for(int j=gy; j>=0; j--) { if(i+x[k]<=gx && j+y[k]<=gy) { d[i+x[k]][j+y[k]]=Math.min(d[i+x[k]][j+y[k]], d[i][j]+c[k]); } } } } int ans=INF; for(int i=0; i<=gx; i++) { for(int j=0; j<=gy; j++) { ans=Math.min(ans, d[i][j]+f*(gx-i+gy-j)); } } out.println(ans); out.close(); scanner.close(); } } class FastScanner { private final InputStream in = System.in; private final byte[] buffer = new byte[1024]; private int ptr = 0; private int buflen = 0; private boolean hasNextByte() { if (ptr < buflen) { return true; } else { ptr = 0; try { buflen = in.read(buffer); } catch (IOException e) { e.printStackTrace(); } if (buflen <= 0) { return false; } } return true; } private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1; } private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126; } public boolean hasNext() { while (hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte(); } public String next() { if (!hasNext()) throw new NoSuchElementException(); StringBuilder sb = new StringBuilder(); int b = readByte(); while (isPrintableChar(b)) { sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } public long nextLong() { if (!hasNext()) throw new NoSuchElementException(); long n = 0; boolean minus = false; int b = readByte(); if (b == '-') { minus = true; b = readByte(); } if (b < '0' || '9' < b) { throw new NumberFormatException(); } while (true) { if ('0' <= b && b <= '9') { n *= 10; n += b - '0'; } else if (b == -1 || !isPrintableChar(b)) { return minus ? -n : n; } else { throw new NumberFormatException(); } b = readByte(); } } public int nextInt() { long nl = nextLong(); if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException(); return (int) nl; } public double nextDouble() { return Double.parseDouble(next()); } }