using namespace std;
int m;
long long s[2000005];
int main(){
	scanf("%d",&m);
	for(int i=1;i<=m;++i){
   		s[i]=s[i-1]+i;
	}
	for(int i=1;i<=m;++i){
		int j=lower_bound(s+1,s+1+m,s[i-1]+m)-s;
		if(s[j]-s[i-1]!=m||j-i+1<2) continue;
		else printf("%d %d\n",i,j); 
	}
	return 0;
}

int j=lower_bound(s+1,s+1+m,s[i-1]+m)-s;

后面为什么要-s啊

蒟蒻诚心求助orz

题号：P1147