#include<bits/stdc++.h> using namespace std; using Int = long long; template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;} template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;} template<typename T> void drop(const T &x){cout<<x<<endl;exit(0);} //INSERT ABOVE HERE signed main(){ Int a,b,c,d; cin>>a>>b>>c>>d; vector<Int> vs({a,b,c,d}); sort(vs.begin(),vs.end()); for(Int i=0;i<3;i++) if(vs[i+1]!=vs[i]+1) drop("No"); drop("Yes"); return 0; }