#include<bits/stdc++.h>

#define LL long long

#define fi first

#define se second

#define mk make_pair

#define PII pair<int, int>

#define PLI pair<LL, int>

#define ull unsigned long long

using namespace std;

const int N =  + ;

const int inf = 0x3f3f3f3f;

const LL INF = 0x3f3f3f3f3f3f3f3f;

const int mod = 1e9 + ;

LL dp[N][N], a[N], hs[N], tot, n;

int main() {

    memset(dp, INF, sizeof(dp));

    scanf("%d", &n);

    for(int i = ; i <= n; i++) {

        scanf("%lld", &a[i]);

        a[i] = a[i] - i;

        hs[tot++] = a[i];

    }

    sort(hs, hs + tot);

    tot = unique(hs, hs + tot) - hs;

    for(int j = ; j < tot; j++) dp[][j] = abs(a[] - hs[j]);

    for(int i = ; i <= n; i++) {

        LL mn = INF;

        for(int j = ; j < tot; j++) {

            mn = min(mn, dp[i - ][j]);

            dp[i][j] = min(dp[i][j], mn + abs(a[i] - hs[j]));

        }

    }

    LL ans = INF;

    for(int j = ; j < tot; j++)

        ans = min(ans, dp[n][j]);

    printf("%lld\n", ans);

    return ;

}

/*

*/