#pragma GCC optimize ("Ofast")
#include<bits/stdc++.h>
using namespace std;
void *wmem;
char memarr[96000000];
template<class T> inline void walloc1d(T **arr, int x, void **mem = &wmem){
  static int skip[16] = {0, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1};
  (*mem) = (void*)( ((char*)(*mem)) + skip[((unsigned long long)(*mem)) & 15] );
  (*arr)=(T*)(*mem);
  (*mem)=((*arr)+x);
}
template<class T1> void sortA_L(int N, T1 a[], void *mem = wmem){
  sort(a, a+N);
}
inline void rd(int &x){
  int k;
  int m=0;
  x=0;
  for(;;){
    k = getchar_unlocked();
    if(k=='-'){
      m=1;
      break;
    }
    if('0'<=k&&k<='9'){
      x=k-'0';
      break;
    }
  }
  for(;;){
    k = getchar_unlocked();
    if(k<'0'||k>'9'){
      break;
    }
    x=x*10+k-'0';
  }
  if(m){
    x=-x;
  }
}
inline void wt_L(char a){
  putchar_unlocked(a);
}
inline void wt_L(const char c[]){
  int i=0;
  for(i=0;c[i]!='\0';i++){
    putchar_unlocked(c[i]);
  }
}
int A[4];
int main(){
  int i;
  wmem = memarr;
  {
    int Lj4PdHRW;
    for(Lj4PdHRW=(0);Lj4PdHRW<(4);Lj4PdHRW++){
      rd(A[Lj4PdHRW]);
    }
  }
  sortA_L(4,A);
  for(i=(0);i<(4);i++){
    if(A[i]!=A[0]+i){
      wt_L("No");
      wt_L('\n');
      return 0;
    }
  }
  wt_L("Yes");
  wt_L('\n');
  return 0;
}
// cLay varsion 20200227-1

// --- original code ---
// int A[4];
// {
//   rd(A(4));
//   sortA(4,A);
//   rep(i,4) if(A[i]!=A[0]+i) wt("No"), return 0;
//   wt("Yes");
// }