#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;
}