#include<stdio.h>

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