    #include<stdio.h>
    int main(){
      int a,b,c,d;
      scanf("%d %d %d %d",&a,&b,&c,&d);
      while(1){
      	if(0 >= (c = c - b)){
        	printf("Yes\n");
            return 0;    
        }
        if(0 >= (a = a - d)){
        	printf("No\n");
      		return 0;    
        }
      }
    }