n, m = map(int, input().split())
arr = list(map(int, input().split()))
score = 0
ps = [arr[0]]
for i in range(1, n):
s = ps[i-1] + arr[i]
ps.append(s)
for i in range(m):
l, r = map(int, input().split())
if (l == 1):
total = ps[r-1]
else:
total = ps[r-1] - ps[l-2]
score = max(score, total+score)
print(score)#include <bits/stdc++.h>
using namespace std;
void solve()
{
int n, m;
cin >> n >> m;
vector <int> v(n+1);
for(int i = 1; i<=n; i++)
{
cin >> v[i];
}
vector<int> cnt(n+1);
for(int i = 1; i<=m; i++)
{
int a, b;
cin >> a >> b;
int sum = 0;
for(int j = a; j<=b; j++)
{
sum = sum + v[j];
}
if(sum>0)
{
for(int x = a; x<=b; x++)
cnt[x]++;
}
}
int ans = 0;
for(int i = 1; i<=n; i++)
{
ans = ans + v[i]*cnt[i];
}
cout << ans << endl;
}
int main()
{
solve();
return 0;
}
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