include iostream include vector include algorithm using namespace std

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#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
int main()
{
int n;
cin >> n;
vector<int> v(n);
bool m = true, ans = true, zero = false, one = false, mz = true;
for (int i = 0; i < n; ++i)
{
cin >> v[i];
if (v[i] > 0)
mz = false;
if (v[i] != 1)
ans = false;
if (v[i] < 0)
m = false;
if (v[i] == 1)
one = true;
if (v[i] == 0)
zero = true;
}
if (ans)
{
cout << "YES" << endl;
return 0;
}
if (one && zero)
{
cout << "YES" << endl;
return 0;
}
if (mz)
{
cout << "NO" << endl;
return 0;
}
if (m)
cout << "NO" << endl;
else
cout << "YES" << endl;
return 0;
}