#include<bits/stdc++.h>
using namespace std;
int main() {
int n;cin>>n;
int A[n];
for(int i=0;i<n;++i)cin>>A[i];
int i=0;
while(i<n-1 && A[i] < A[i+1]) ++i;
if( i != 0 && A[i]==A[i-1]){cout<<"false";return 0;}
while(i<n-1 && A[i] > A[i+1]) ++i;
if(i==n-1)cout<<"true";
else cout<<"false";
return 0;
}
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