#include <bits/stdc++.h>
using namespace std;
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()
#define valid(y,x,h,w) (0<=y&&y<h&&0<=x&&x<w)
#define tpl(...) make_tuple(__VA_ARGS__)
const int INF = 0x3f3f3f3f;
const double EPS = 1e-8;
const double PI = acos(-1);
typedef long long ll;
typedef pair<ll,ll> pii;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T>ostream&operator<<(ostream &o,const vector<T>&t){o<<'[';FOR(i,t){if(i!=t.begin())o<<',';o<<*i;}return o<<']';}
template<class S,class T>ostream&operator<<(ostream &o,const pair<S,T>&t){return o<<'('<<t.first<<','<<t.second<<')';}
template<int N,class Tp>void output(ostream&,const Tp&){}
template<int N,class Tp,class,class ...Ts>void output(ostream &o,const Tp&t){if(N)o<<',';o<<get<N>(t);output<N+1,Tp,Ts...>(o,t);}
template<class ...Ts>ostream&operator<<(ostream&o,const tuple<Ts...>&t){o<<'(';output<0,tuple<Ts...>,Ts...>(o,t);return o<<')';}
template<class T>void output(T t,char z=10){if(t<0)t=-t,putchar(45);int c[20];
  int k=0;while(t)c[k++]=t%10,t/=10;for(k||(c[k++]=0);k;)putchar(c[--k]^48);putchar(z);}
template<class T>void outputs(T t){output(t);}
template<class S,class ...T>void outputs(S a,T...t){output(a,32);outputs(t...);}
template<class T>void output(T *a,int n){REP(i,n)output(a[i],i!=n-1?',':10);}
template<class T>void output(T *a,int n,int m){REP(i,n)output(a[i],m);}
template<class T>bool input(T &t){int n=1,c;for(t=0;!isdigit(c=getchar())&&~c&&c-45;);
  if(!~c)return 0;for(c-45&&(n=0,t=c^48);isdigit(c=getchar());)t=10*t+c-48;t=n?-t:t;return 1;}
template<class S,class ...T>bool input(S&a,T&...t){input(a);return input(t...);}

ll a[100000];
ll b[100000];

ll t[100000];

int main() {
  ll n;
  ll m,C;
  while(input(n,m,C)) {
    REP(i,n) {
      input(a[i]);
      b[i] = a[i];
    }
    reverse(b,b+n);
    ll low = -1, high = n+1;
    while(low+1<high) {
      ll mid = (low+high)/2;
      deque<pii> D;
      REP(i,n) {
        while(D.size()) {
          pii &p = D.front();
          if (p.second < i-mid) {
            D.pop_front();
          } else break;
        }
        while(D.size()) {
          pii &p = D.back();
          if (p.first - (i-p.second)*C < a[i]) {
            D.pop_back();
          } else break;
        }
        D.push_back(pii(a[i], i));
        pii &p = D.front();
        t[i] = p.first - (i-p.second)*C;
        // REP(j,D.size()) {
        //   assert(D[j].first-(i-D[j].second)*C <= t[i]);
        // }
      }
      // REP(i,n) {
      //   ll tmp = a[i];
      //   for (int j=max(0LL,i-mid); j<=i; ++j) {
      //     chmax(tmp, a[j] - abs(i-j)*C);
      //   }
      //   assert(tmp == t[i]);
      // }      
      D.clear();
      REP(i,n) {
        while(D.size()) {
          pii &p = D.front();
          if (p.second < i-mid) {
            D.pop_front();
          } else break;
        }
        while(D.size()) {
          pii &p = D.back();
          if (p.first - (i-p.second)*C < b[i]) {
            D.pop_back();
          } else break;
        }
        D.push_back(pii(b[i], i));
        pii &p = D.front();
        chmax(t[n-i-1], p.first - (i-p.second)*C);
      }
      ll sum = 0;
      REP(i,n) sum += t[i];
      
      // cout << mid << " " << sum << endl;
      // output(t,n);
      if (sum >= m) {
        high = mid;
      } else {
        low = mid;
      }
    }
    if (high == n+1) {
      cout << -1 << endl;
    } else {
      cout << high << endl;
    }
  
  }
}


Measured memory_bytes: 3520