求大佬解惑

#include <bits/stdc++.h>
using namespace std;

int l,m;
int u,v;

int main(){
//	freopen("123.txt","r",stdin);
//	freopen("123.txt","w",stdout);
	scanf("%d%d",&l,&m);
	int cut=0;
	for(int i=1;i<=m;i++){
		scanf("%d%d",&u,&v);
		l-=v-u;
		cout<<l<<endl;
	}
	printf("%d",l);
	return 0;
}