#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 k1,k2,a=1,b=1,c,sum=0;
cin>>k1>>k2;
for (int i=3;i<k1;i++)
{
c=a+b;
a=b;
b=c;

}
for (int i=k1;i<=k2;i++)
{
if(i<=2)
sum=sum+1;
else
{
c=a+b;
a=b;
b=c;
sum=sum+c;
}
}
cout<<sum;
return 0;
}
包对

#include<bits/stdc++.h>
using namespace std;
int main( )
{
long long k1,k2,a=1,b=1,c,sum=0;
cin>>k1>>k2;
for (int i=3;i<k1;i++)
{
c=a+b;
a=b;
b=c;

}
for (int j=k1;j<=k2;j++)
{

c=a+b;
a=b;
b=c;
sum=sum+c;
}
cout<<sum;
return 0;

}

#include<bits/stdc++.h>
using namespace std;
int main()
{
int k1,k2,a=1,b=1,c,sum=0;
cin>>k1>>k2;
for (int i=k1;i<=k2;i++)
{
if(i<=2)
sum=sum+1;
else
{
c=a+b;
a=b;
b=c;
sum=sum+c;
}
}
cout<<sum;
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;
}