#include <bits/stdc++.h>
using namespace std;
template <typename T, typename U>
inline void smin(T &a, U b) {
  if (a > b) a = b;
}
template <typename T, typename U>
inline void smax(T &a, U b) {
  if (a < b) a = b;
}
template <class T>
inline void gn(T &first) {
  char c, sg = 0;
  while (c = getchar(), (c > '9' || c < '0') && c != '-')
    ;
  for ((c == '-' ? sg = 1, c = getchar() : 0), first = 0; c >= '0' && c <= '9';
       c = getchar())
    first = (first << 1) + (first << 3) + c - '0';
  if (sg) first = -first;
}
template <class T>
inline void print(T first) {
  if (first < 0) {
    putchar('-');
    return print(-first);
  }
  if (first < 10) {
    putchar('0' + first);
    return;
  }
  print(first / 10);
  putchar(first % 10 + '0');
}
template <class T, class T1>
inline void gn(T &first, T1 &second) {
  gn(first);
  gn(second);
}
template <class T, class T1, class T2>
inline void gn(T &first, T1 &second, T2 &z) {
  gn(first);
  gn(second);
  gn(z);
}
int power(int a, int b, int m, int ans = 1) {
  for (; b; b >>= 1, a = 1LL * a * a % m)
    if (b & 1) ans = 1LL * ans * a % m;
  return ans;
}
inline unsigned int myrand(int n) {
  unsigned int u = rand() % n;
  int c = rand() % 10;
  u ^= u << c;
  u ^= (u << 7) & 263692864;
  u ^= (u << 15) & 402273075;
  u %= n;
  return u;
}
int sum[100011];
int a[100011];
map<int, int> cnt;
int main() {
  int k, b, n;
  cin >> k >> b >> n;
  k--;
  long long ans = 0;
  if (b == 0) {
    for (int i = 1; i <= n; i++) {
      gn(a[i]);
    }
    for (int i = 1, j = 1; i <= n; i = j) {
      if (a[j]) {
        j++;
        continue;
      }
      while (j <= n and a[j] == a[i]) j++;
      ans += (long long)(j - i) * (j - i + 1) / 2;
    }
    cout << ans << endl;
    return 0;
  }
  if (b == k) b = 0;
  cnt[0]++;
  for (int i = 1; i <= n; i++) {
    gn(a[i]);
    sum[i] = (sum[i - 1] + a[i]) % k;
    ans += cnt[(sum[i] - b + k) % k];
    cnt[sum[i]]++;
  }
  if (b == 0)
    for (int i = 1, j = 1; i <= n; i = j) {
      if (a[j]) {
        j++;
        continue;
      }
      while (j <= n and a[j] == a[i]) j++;
      ans -= (long long)(j - i) * (j - i + 1) / 2;
    }
  cout << ans << endl;
  return 0;
}
