# include<iostream> # include<cstdio> # include<iomanip> using namespace std; int main(){ int L,M,a,b,c=0; cin>>L>>M; for(int i=1;i<=M;i++) { cin>>a>>b; if(a<b){ c=a; a=b; b=c; } L=L-(a-b); } cout<<L; return 0; }