#include <iostream> using namespace std; int a[10005]; int main () { int n,m; cin>>n>>m; for(int i=0;i<=n;i++) a[i] =1; //有一棵树 for(int j=1;j<=m;j++) { int a1,b1; cin>>a1>>b1; for(int k=a1;k<=b1;k++) a[k] =0; //砍树; } int res =0; for(int i=0;i<=n;i++) if(a[i]==1) res++; cout<<res; return 0; }