C++ :

#include<bits/stdc++.h>
using namespace std;
long long n,m,x,y,a[2000000+5],s[2000000+5],mx;
long long li,ri;
int main(){
//	freopen("10.in","r",stdin);
//	freopen("10.out","w",stdout);
    cin>>n>>m;
    for(int i=1;i<=n;i++)
    {
    	scanf("%lld",&a[i]);
    	if(a[i]<0) a[i]=0;
    	a[i+n]=a[i];
    }
    for(int i=1;i<=2*n;i++)
        s[i]=s[i-1]+a[i];
    while(m--)
    {
    	scanf("%lld%lld",&x,&y);
    	li=x;
    	ri=x+y-1;
    	if(s[ri]-s[li-1]>mx) mx=s[ri]-s[li-1];
    	//cout<<mx<<endl;
    }
    cout<<mx;
    return 0;
}