#include <stdio.h>

int main(void) {
    int A, B, C, D;
    int sum_A, sum_C;
    scanf("%d %d %d %d", &A, &B, &C, &D);
    sum_A = A;
    sum_C = C;
    while(1) {
        sum_C = sum_C - B;
        if(sum_C <= 0) {
            printf("Yes\n");
            break;
        }
        
        sum_A = sum_A - D;
        if(sum_A <= 0){
            printf("No\n");
            break;
        }
    }
    return 0;
}