#include <stdio.h>

int main(int argc, const char * argv[]) {
    // insert code here...
    int A,B,C,D;
    printf("\n");
    scanf("%d %d %d %d",&A,&B,&C,&D);
    while(1){
        C=C-B;
        if(C<=0){
            printf("Yes\n");
            break;
        }
        A=A-D;
        if(A<=0){
            printf("No\n");
            break;
        }
        }
    
    
    return 0;
}
