using namespace std;
const int N=109;
int n,m,x[N],y[N];
int ans;
int main() {
	cin>>n>>m;
	while(m--){
		for(int i=1;i<=m;i++)
		cin>>x[i]>>y[i];
	sort(x+1,x+1+m);
	}
	for(int i=1;i<=m;i++){
if(x[i]==0&&y[i]==n)cout<<"0";
while(x[i+1]<y[i]){
	if(y[i+1]<y[i])
    y[i]=y[i];
	if(y[i+1]>y[i])
	y[i]=y[i+1];
ans+=y[i]-x[i];
}
if(x[i+1]>=y[i])
ans+=y[i]-x[i]+1;
cout<<ans;
}
return 0;
}