#include <stdio.h>
#include <stdlib.h>

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");

    return EXIT_SUCCESS;
}
