#include<bits/stdc++.h>
using namespace std;
/*
int main()
{
int n,x,a[6000];
cin>>n;
for(int i=1;i<=n;i++)
{
cin>>a[i];
}
cin>>x;
for(int i=1;i<=n;i++)
{
if(x==a[i])
{
cout<<i;
}
}
}
*/
int main()
{
int n,x,a[6000]={0},mid=2;
cin>>n;
for(int i=1;i<=n;i++)
{
cin>>a[i];
}
cin>>x;
int left=1;
int right=n;
int r=-1;
while(mid!=0)
{
mid=(left+right)/2;
if(a[mid]==x)
{
r=mid;
break;
}
else if(x<a[mid])
{
right=mid-1;
}
else if(x>a[mid])
{
left=mid+1;
}
}
if(r==-1)
{
cout<<-1;
}
else
{
cout<<r;
}
}
/*
int a[1000000],x;
int fun(int left,int right);
int mid=2;
int main()
{
int n,r;
left,right;
cin>>n;
for(int i=1;i<=n;i++)
{
cin>>a[i];
}
cin>>x;
r=fun(1,n);
if(r==-1)
{
cout<<-1;
}
else
{
cout<<r;
}
}
int fun(int left,int right)
{
if(mid!=0)
{
mid=(left+right)/2;
if(x<a[mid])
{
return fun(left,mid-1);
}
else if(x>a[mid])
{
return fun(mid+1,right);
}
else
{
return mid;
}
}
else
{
return -1;
}
}
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