#include<bits/stdc++.h>
#define N 100005
#define int long long
#define db double
#define fo(i,l,r) for(int i=l;i<=r;i++)
#define rf(i,r,l) for(int i=r;i>=l;i--)
using namespace std;
int T,n,m,k,a[N],op,x,y,z,ans,last;
void swap(int &x,int &y){int t=x;x=y;y=t;}
int max(int x,int y){return x>y?x:y;}
int min(int x,int y){return x<y?x:y;}
void ckmax(int &x,int y){if(y>x)x=y;}
void ckmin(int &x,int y){if(y<x)x=y;}
int fp(int a,int n,int mod){
    int ans=1;
    while(n){
        if(n&1)ans=ans*a%mod;
        a=a*a%mod;
        n>>=1;
    }
    return ans;
}
int gcd(int a,int b){return b?gcd(b,a%b):a;}
int po(int x){return x*x;}
int sub(int x,int y){return x>y?x-y:y-x;}
int ab(int x){return x<0?-x:x;}
int read(){
    int sum=0;bool f=0;char c=getchar();
    for(;c<48||c>57;c=getchar())if(c==45)f=1;
    for(;c>=48&&c<=57;c=getchar())sum=sum*10+(c&15);
    return f?-sum:sum;
}
signed main(){
    freopen("defeat.in","r",stdin);freopen("defeat.out","w",stdout);
    n=read();k=read();read();
    fo(i,1,n)a[i]=read();
    int now=0;
    fo(i,1,n){
        x=k-(a[i]+now);
        ans+=ab(x);
        now+=x;
    }
    printf("%lld",ans);
    return 0;
}