#include <bits/stdc++.h>

using namespace std;

const int maxn=5e4; 
int n,m,a[maxn+5]; 
bitset<maxn+5> B[maxn+5],suf[maxn+5],pre[maxn+5]; 
int pos[maxn+5]; 
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cin>>n>>m;
    for (int i=1;i<=n;i++) {
        cin>>a[i]; 
        pos[a[i]]=i; 
    }
    bitset<maxn+5> S;
    for (int i=1;i<=n;i++) S[i]=1;
    for (int i=1;i<=n;i++) {
        S[pos[i]]=0;
        B[pos[i]]=(S>>pos[i]); 
    }
    long long ans=0; 
    for (int i=m;i<=n;i+=m) {
        suf[1]=pre[1]=B[i]; 
        for (int j=2;j<=m;j++) {
            suf[j]=suf[j-1]&B[i-j+1];
            pre[j]=pre[j-1]&B[i+j-1];  
        }
        for (int j=1;j<=m;j++) {
            ans+=(suf[j]&pre[m-j+1]).count(); 
        }
    }
    cout<<ans<<'\n'; 
    return 0; 
}