#include <stdio.h> #include <vector> using namespace std; int main(){ vector<int> tree; int l,m; int low,high; scanf("%d%d",&l,&m); for(int i=0;i<=l;++i){ tree.push_back(1); } for(int j=0;j<m;++j){ scanf("%d%d",&low,&high); for(int i=low;i<=high;++i){ tree[i]=0; } } int count=0; for(int i=0;i<=l;++i){ if(tree[i]==1){++count;} } printf("%d",count); return 0; }