#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
int cmp(const void *a,const void *b){
    if(*(int*)a>*(int*)b){return 1;}
    else if(*(int*)a<*(int*)b){return -1;}
    else {return 0;}
}
int min(int a,int b){

    if(a>=b){return b;}
    return a;
}
//cww
int main(void){
int a[4];
int min=99;
scanf("%d %d %d %d",&a[0],&a[1],&a[2],&a[3]);

qsort(a,4,sizeof(int),cmp);
if(a[1]==a[0]+1&&a[2]==a[1]+1&&a[3]==a[2]+1){printf("Yes\n");}
else{printf("No\n");}


}