int main(void){
    int A, B, C, D;
    scanf("%d %d %d %d",&A, &B, &C, &D);
    while(A > 0 && C > 0){
        C -= B;
        if(C <= 0){
            break;
        }
        A -= D;
    }
    if(A > 0){
        printf("Yes\n");
    }
    else{
        printf("No\n");
    }
}