#include <cstdio> #include <cstring> #include <iostream> #include <algorithm> using namespace std; int n, m, a[100010], v[100010], V[100010],sum,V2[100010],ans; bool check(int x) { int i; for (i = x - n + 1; i >= 1; i -= n) if (!V2[i]) return false; i += n; if (i - 1 > 0 && !V[i - 1]) return false; return true; } int main() { scanf("%d%d", &n, &m); for (int i = 1; i <= m; i++) scanf("%d", &a[i]); for (int i = 1; i <= min(n, m); i++) { v[a[i]]++; if (v[a[i]] == 2) sum++; if (!sum) V[i] = 1; } if (!sum) V2[1] = 1; for (int i = n + 1; i <= m; i++) { v[a[i]]++; if (v[a[i]] == 2) sum++; v[a[i - n]]--; if (v[a[i - n]] == 1) sum--; if (!sum) V2[i - n + 1] = 1; } memset(v, 0, sizeof(v)); sum = 0; int i = 0; for (i = m; i >= 1; i--) { v[a[i]]++; if (v[a[i]] >= 2) break; } for (int j = m; j > max(0, m - n); j--) if (i <= j && check(j)) ans++; if (ans) printf("%d\n", (n >= m && ans == m ? n : ans)); else printf("0\n"); return 0; }