#include <stdio.h>

void main() {

    int A, B, C, D;
    char buf[1000];

    fgets(buf, sizeof(buf), stdin);
    sscanf(buf, "%d %d %d %d\n", &A, &B, &C, &D);

    while (0 < A && 0 < C) {
        C -= B;
        if (C <= 0) {
            break;
        } 
        A -= D;
    }
    if (A > 0) {
        printf("Yes");
    }
    else {
        printf("No");
    }
    return;
}