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

#define MAX(a,b) (a > b) ? a : b
#define MIN(a,b) (a < b) ? a : b
const int inf = 1000000000; // 10^9

int com_asc_int(const void *n1,const void *n2){
   if(*(int*)n1 > *(int*)n2)return 1;
   else if(*(int*)n1 < *(int*)n2)return -1;
   else return 0;
}

int main (){
   int a[4];for(int i = 0;i < 4;i++)scanf("%d",&a[i]);
   qsort(a,4,sizeof(int),com_asc_int);
   if((a[1] == a[0] + 1 )&&(a[2] == a[1] + 1 )&&(a[3] == a[2] + 1 ))printf("Yes");
   else printf("No");
}