#include using namespace std; using ll = long long; using P = pair; #define rep(i, n) for(int (i)=0;(i)<(n);(i)++) #define chmin(x, y) x = min(x, y) #define chmax(x, y) x = max(x, y) bool custom1 (pair a, pair b) { return (a.first < b.first); } bool custom2(pair a, pair b) { return (a.second < b.second); } const int MAX = 200005; const long long MOD = 1000000007; const long long MODMOD = 998244353; long long fac[MAX], finv[MAX], inv[MAX]; void COMinit() { fac[0] = fac[1] = 1; finv[0] = finv[1] = 1; inv[1] = 1; for (int i = 2; i < MAX; i++){ fac[i] = fac[i - 1] * i % MOD; inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD; finv[i] = finv[i - 1] * inv[i] % MOD; } } long long COM(int n, int k){ if (n < k) return 0; if (n < 0 || k < 0) return 0; return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD; } long long modpow(long long a, long long n, long long mod) { long long res = 1; while (n > 0) { if (n & 1) res = res * a % mod; a = a * a % mod; n >>= 1; } return res; } long long modinv(long long a, long long m) { long long b = m, u = 1, v = 0; while (b) { long long t = a / b; a -= t * b; swap(a, b); u -= t * v; swap(u, v); } u %= m; if (u < 0) u += m; return u; } long long gcd(long long a, long long b) { if(a % b == 0) return b; else return gcd(b, a % b); } int main() { vector input(4); rep(i, 4) cin >> input[i]; sort(input.begin(), input.end()); bool yes = true; rep(i, 3) { if(input[i] + 1 == input[i+1]) continue; else { yes = false; break; } } if(yes) cout << "Yes" << endl; else cout << "No" << endl; }