    #include <stdio.h>
    #include <string.h>

    int main(void)
    {
        int A,B,C,D;
        int x,y;
        scanf("%d %d %d %d",&A,&B,&C,&D);
        x = (A+D-1)/D;
        y = (C+B-1)/B;
        if(x >= y){printf("Yes\n");}
        else{printf("No\n");}
        return 0;
    }