1088

#include <iostream>#include <stdio.h>using namespace std;int L,M;int tree[10001];int main(){    while(scanf("%d %d",&L,&M)!=EOF){        for(int i = 0 ; i <= 10000; i ++){            tree[i] = 0;        }        for(int i = 0 ; i < M ; i ++){            int x,y;            scanf("%d %d",&x,&y);            for(int i = x; i <=y ; i ++){                tree[i] = 1;            }        }        int number = 0;        for(int i = 0; i <=L; i ++ ){            if(tree[i]==0)             number ++;        }        printf("%d\n",number);    }    return 0;}