View Code of Problem 18

#include<iostream>
#include<vector>

using namespace std;

int main()
{
    int n;
    while(cin>>n)
    {
        int a[n+1];
        a[1]=0;a[2]=0;a[3]=1;
        for(int i=4;i<=n;i++)
            a[i]=a[i-2]+a[i-1]+1;
        cout<<a[n]<<endl;
    }
}