#include<bits/stdc++.h>
using namespace std;
int a[10005];
int main()
{
    int x,y,sum=0;
    cin>>x>>y;
    for(int i=1;i<=y;i++)
        cin>>a[i];
    a[1]=1;
    a[2]=1;
    for(int i=3;i<=y;i++)
        a[i]=a[i-2]+a[i-1];
    for(int i=x;i<=y;i++)
        sum+=a[i];
    cout<<sum<<endl;
    return 0;
} 

#include<bits/stdc++.h>
using namespace std;
int a,b,sum=0,fei[1000005]{0,1,1};
int main()
{
    cin>>a>>b;
    for(int i=3;i<=b;i++)
        fei[i]=fei[i-1]+fei[i-2];
    for(int i=a;i<=b;i++)
        sum=sum+fei[i];
    cout<<sum;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int m,n,c,a,b,x,y,z,sum1=2,sum2=2;
    cin>>m>>n;
    a=1;
    b=1;
    if(m<3)
        sum1=m-1;
    else
    for(int i=3;i<=m-1;i++)
    {
        c=a+b;
        a=b;
        b=c;
        sum1+=c;
    }
    x=1;
    y=1;
    if(n<3)
        sum2=n;
    else
    for(int i=3;i<=n;i++)
    {
        z=x+y;
        x=y;
        y=z;
        sum2+=z;
    }
    cout<<sum2-sum1;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
int n,a,b,c,i;
cin>>n;
a=1;
b=1;
i=3;
while(i<=n)
{
c=a+b;
a=b;
b=c;
i=i+1;
}
cout<<a+b+c-1;
return 0;
}