input()
a=input()+' '
print(a.count('1')+max(len([*filter(None,a.split('0 '))])-1,0))
#include <bits/stdc++.h>
#define deb(x) cout<<endl<<#x <<" = "<<x<<endl<<endl
using namespace std;
typedef long long ll;
typedef double dd;
int main()
{
ll tt; tt=1;
while(tt--)
{
ll n; cin>>n;
ll a[n];
for(ll i=0;i<n;i++) cin>>a[i];
for(ll i=1;i<n-1;i++) if(a[i-1]==1 && a[i+1]==1) a[i]=1;
ll ans=0,buff=0;
for(ll i=0;i<n;i++){
if(a[i]){
buff++;
}
else if(buff){
ans+=buff;
ans++;
buff=0;
}
}
if(buff){
ans+=buff;
ans++;
}
cout<<max(0ll,--ans)<<endl;
}
}
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