#include<bits/stdc++.h>
#define int long long
#define endl '\n'
using namespace std;
const int N=50005;
int n,m,a[N],r;
bitset<N> f[N],g[N],k,l;
int z[N];
signed main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
	cin>>n>>m;
	for(int i=1;i<=n;i++) cin>>a[i],z[a[i]]=i;
	for(int i=n;i;--i){
		f[z[i]]=l<<z[i];
		l.set(z[i]);
	}
	for(int i=m;i<=n;i+=m){
		k.set();
		for(int j=1;j<=m;j++){
			k&=f[i-j+1];
			g[i-j+1]=k;
		}
		k.set();
		for(int j=1;j<=m&&i+j-1<=n;j++){
			k&=f[i+j-1];
			r+=(k&g[i-(m-j+1)+1]).count();
		}
	}
	cout<<r;
    return 0;
}