#include<stdio.h>
int main()
{
    int A, B, C, D, x, y;
    scanf("%d %d %d %d", &A, &B, &C, &D);
    for(x=C; x>=0 ; x-=B){
        if(x<=0){
            printf("Yes\n");
            break;
        }
        else{
            y=A-D;
            if(y<=0){
                printf("No\n");
                break;
            }
        }
    }

    return 0;
}
