#include<stdio.h>
#include<math.h>


#define N 81

int main(void){
    int x = 0;
    int y = 0;
    int n = 0;
    int a[N];
    //int flag[10];
    int i = 0;

    scanf("%d %d", &x, &y);
    scanf("%d", &n);
    for(i = 1; i <= n; i++){
        scanf("%d", &a[i]);
    }

    for(i = 1; i <= n-1; i++){
        if(((1.0/(double)x)*(double)a[i]-(1.0/(double)y)*(double)a[i])*y+(double)a[i] > (double)a[i+1]){
            printf("NO\n");
            return 0;
        }
    }
    printf("YES\n");


    return 0;
}