#include<bits/stdc++.h>
#define REP(i,n) for(int i=0,i##_len=(n);i<i##_len;++i)
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
#define All(x) (x).begin(),(x).end()
using namespace std;
using ll = long long;

int main(){
    int N;cin>>N;
    vector<int> B(N);
    REP(i, N) cin >> B[i];
    int l=0;
    ll ans=0;
    REP(i,N){
        while(l<N&&B[l]!=0){
            l++;
        }
        if(B[i]>0){
            while(l<N&&B[i]>1){
                while(B[l]!=0) l++;
                B[l]++;
                B[i]--;
                ans+=abs(i-l);
            }
        }
    }
    cout<<ans<<endl;
}