#include <bits/stdc++.h>
using namespace std;
inline int read() {
  int x = 0;
  char s = getchar();
  while (!isdigit(s)) s = getchar();
  while (isdigit(s)) x = x * 10 + s - '0', s = getchar();
  return x;
}
const int N = 1e5 + 5;
const long double eps = 1e-9;
int n, m, p, hd, tl, d[N];
long long t[N], s[N], f[N], g[N];
long double sl(int i, int j) {
  return (long double)(g[j] + s[j] - g[i] - s[i]) / (j - i);
}
int main() {
  cin >> n >> m >> p;
  for (int i = 2; i <= n; i++) cin >> d[i], d[i] += d[i - 1];
  for (int i = 1, h; i <= m; i++) cin >> h >> t[i], t[i] -= d[h];
  sort(t + 1, t + m + 1);
  if (t[m] < 0) t[++m] = 0;
  for (int i = 1; i <= m; i++) s[i] = s[i - 1] + t[i];
  memset(g, 0x3f, sizeof(g)), g[0] = 0;
  for (int z = 1; z <= p; z++) {
    d[hd = tl = 1] = 0;
    for (int i = 1; i <= m; i++) {
      while (hd < tl && sl(d[hd], d[hd + 1]) + eps <= t[i]) hd++;
      int j = d[hd];
      f[i] = g[j] + (i - j) * t[i] - s[i] + s[j];
      while (hd < tl && sl(d[tl - 1], d[tl]) - eps >= sl(d[tl], i)) tl--;
      d[++tl] = i;
    }
    memcpy(g, f, sizeof(f));
  }
  cout << f[m] << endl;
  return 0;
}
