input = require('fs').readFileSync('/dev/stdin','utf8');
tmp = input.split(' ');
THP = parseInt(tmp[0],10);
TAP = parseInt(tmp[1],10);
AHP = parseInt(tmp[2],10);
AAP = parseInt(tmp[3],10);
while(THP > 0 && AHP > 0) {
  AHP = AHP - TAP;
  if(AHP <= 0) { console.log('Yes'); break; }
  THP = THP - AAP;
  if(THP <= 0) { console.log('No'); break; }
}
