function main(arg) {
  var [A, B, C, D] = arg[0].split(' ').map(v => v - 0);
  
  while (A > 0 || C > 0) {
  	C -= B;
    if(C <= 0){
      console.log('Yes')
      break;
    }
    A -= D;
    if(A <= 0) {
      console.log('No')
      break;
    }
  }
}

main(require("fs").readFileSync("/dev/stdin", "utf8").trim().split('\n'));
