#include<iostream>
#include<vector>
#include<queue>
using namespace std;
int N,M,C;
int A[2<<17];
vector<pair<int,int> >G[2<<17];
long dp[2<<17];
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cin>>N>>M>>C;
	long sum=0;
	for(int i=0;i<N;i++)
	{
		cin>>A[i];
		G[i].push_back(make_pair(i+1,A[i]));
		G[i+1].push_back(make_pair(i,A[i]));
		sum+=A[i];
	}
	for(int i=0;i<M;i++)
	{
		int l,r;cin>>l>>r;
		G[l-1].push_back(make_pair(r,C));
	}
	for(int i=1;i<=N;i++)dp[i]=9e18;
	priority_queue<pair<long,int> >Q;
	Q.push(make_pair(0L,0));
	while(!Q.empty())
	{
		int u=Q.top().second;
		long c=-Q.top().first;
		Q.pop();
		if(dp[u]<c)continue;
		for(pair<int,int>e:G[u])
		{
			int v=e.first;
			long nc=c+e.second;
			if(dp[v]>nc)
			{
				dp[v]=nc;
				Q.push(make_pair(-nc,v));
			}
		}
	}
	cout<<sum-dp[N]<<endl;
}