#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() using namespace std; int main(){ int l,m,i,sum,j; cin>>l>>m; int a[m*2+1],b[l+1]={}; for(i=1;i<=m*2;i+=2){ cin>>a[i]>>a[i+1]; } for(i=1;i<=m*2;i+=2){ for(j=a[i];i<=a[i+1];i++){ if(j==0){ j=1; } } } for(i=1;i<=l;i++){ if(i==0){ sum++; } } cout<<sum; return 0; }