差分85pts玄关

#include <bits/stdc++.h>

#define ll long long
#define ris(x,y,z) for(ll x=y;x<z+1;++x)

using namespace std;

int main(){
    int N,K;
    cin>>N>>K;
    vector<ll> A(N);
    ris(i,0,N-1)
        cin>>A[i];
    vector<ll> diff(N+1);
    ll res=0;
    ll curr=0;
    ris(i,0,N-1){
        curr+=diff[i];
        ll act=A[i]-curr;
        if(i<=N-K){
            ll ops=act;
            res+=ops;
            curr+=ops;
            diff[i+K]-=ops;
        }
        else
            res+=act;
    }
    cout<<res<<endl;
    return 0;
}