#include <cstdio>
typedef long long ll;
inline void in(ll &x) {
	x=0;
	ll f=1;
	char ch=getchar();
	while (ch<'0'||ch>'9') {
		if (ch=='-') f=-1;
		ch=getchar();
	}
	while (ch>='0'&&ch<='9') x=x*10+ch-'0',ch=getchar();
	x*=f;
}
inline void out(ll x) {
	if (x<0) putchar('-'),x=-x;
	if (x>9) out(x/10);
	putchar(x%10+'0');
}
ll n;
bool ok[10005];
int main() {
	in(n);
	for (ll i=1; i<=n; ++i) {
		ll x;
		in(x);
		if (x<1||x>n||ok[x]) {
			puts("No");
			return 0; 
		}	
		ok[x]=1;
	}
	puts("Yes");
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
 int N;
  cin >> N;
  if(N>=0)cout<<N;
  else cout<<0;
  return 0;
}