# include<iostream> # include<cmath> using namespace std; int l,m,a[100001]={0},z,y,sum; int main(){ cin>>l; cin>>m; for(int i=1;i<=m;i++){ cin>>z>>y; for(int j=z;j<=y;j++) a[j]=1; } for(int i=0;i<=l;i++){ if(a[i]==0){ sum++; } } cout<<sum; return 0; }