#include<stdio.h>

int main(void){
    int A,B,C,D;
    int i=-1;
    scanf("%d %d %d %d",&A,&B,&C,&D);

    for(;;){
        C=C-B;
        if(C<=0){
            i = 0;
            break;
        }

        A=A-D;
        if(A<=0){
            i = 1;
            break;
        }
    }

    if(i == 0)
        printf("Yes");
    else
        printf("No");
    
    return 0;
    
}
