#include <iostream>
using namespace std;
int
t[201], r[201], n, ans[201];
void
__read__()
{
cin >> n;
for( int i = 1; i <= n; i++ )
cin >> t[i];
for( int i = 1; i < n; i++ )
cin >> r[i];
}
void
__init__()
{
for( int i = 1; i <= n; i++ )
ans[i] = 9999999;
}
void
__dp__()
{
for( int i = 1; i <= n; i++ )
if( t[i] + t[i + 1] > r[i] )
{
ans[i] = r[i] + ans[i - 1];
ans[++i] = ans[i - 1];
}
else
ans[i] = ans[i - 1] + t[i];
}
void
__outp__()
{
cout << ans[n] << endl;
}
int
main()
{
__read__();
__init__();
__dp__();
__outp__();
return 0;
}