#include<bits/stdc++.h>
using namespace std;
int read(){
	int x=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
	return x*f;
}
int a[1000000];
int main(){
//	freopen("turnback.in","r",stdin);
//	freopen("turnback.out","w",stdout);
	int n,m,ans=0;
	cin>>n>>m;
	for(int i=1;i<=n-2;i++)ans+=read();
	cout<<ans<<"\n";
	return 0;
}