#include<stdio.h>

int main() {
    int A, B, C, D;
    scanf("%d%d%d%d",&A,&B,&C,&D);
    
    int RemainA = A;
    int RemainC = C;
    while (1) {
        /*Takahasi attack*/
        RemainC -= B;
        if (RemainC <= 0) {
            printf("Yes\n");
            break;
        }
        /*Aoki's attack*/
        RemainA -= D;
        if (RemainA <= 0) {
            printf("No\n");
            break;
        }
    }
    return 0;
}