#include <bits/stdc++.h>
#define quick ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define F first
#define S second
#define pb push_back
#define mp make_pair
#define ll long long
#define ull unsigned ll
#define pii pair <int,int>
#define pll pair <ll,ll>
#define INF 1000000000
#define mod 1000000007
#define size(a) ((int)(a.size()))
using namespace std;
void solv()
{
	int n;
	cin>>n;
	int t[n];
	for(int i=0;i<n;i++)
    {
        cin>>t[i];
    }
    int ans=0;
    int a=0,b=0;
    for(int i=0;i<n;i++)
    {
        if(t[i]) a=1;
        else b=1;
        if(a&b)
        {
            ans++;
            a=b=0;
        }
    }
    cout<<ans<<endl;
}
int main()
{
	quick
	int TT=1; //   cin>>TT;
	while(TT--)  solv();

	return 0;
}