process.stdin.resume();
process.stdin.setEncoding('utf8');

var lines = []
var reader = require('readline').createInterface({
  input: process.stdin,
  output: process.stdout
});

reader.on('line', (line) => {
  lines.push(line);
});

reader.on('close', () => {
 var abcd = lines[0].split(' ');
 var a = Number(abcd[0]);
 var b = Number(abcd[1]);
 var c = Number(abcd[2]);
 var d = Number(abcd[3]);

 while(true){
   c = c - b;
   if(c <= 0){
     console.log("Yes");
     break;
   }
   a = a - d;
   if(a <= 0){
     console.log("No");
     break;
   }
 }
});