#include<iostream>
#include<cstdio>
#define ll long long
using namespace std;
ll n,d,a,b,ans;
ll read()
{ll aa=0,bb=1;char cc=getchar();while(cc>'9'||cc<'0'){if(cc=='-') bb=-1;cc=getchar();}while(cc>='0'&&cc<='9'){aa=(aa<<3)+(aa<<1)+(cc^'0');cc=getchar();}return aa*bb;
}
bool check(ll x)
{ll ha=(x-a)/d,hb=(x-b)/d;if(d*ha<x-a) ha++;if(d*hb<x-b) hb++;if(ha+hb<=n-1) return true;return false;
}
int main()
{n=read();d=read();a=read();b=read();if(n==2){printf("%lld\n",max(a,b));return 0;}ll l=max(a,b),r=d*(n-1),mid;while(l<=r){mid=(l+r)>>1;if(check(mid)){ans=mid;l=mid+1;}else r=mid-1;}printf("%lld\n",ans);return 0;
}

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<map>
#include<queue>
#include<stack>
#include<set>
#define ll long long
using namespace std;
struct node
{ll x,id,l,r;
}h[100100];
ll n,Q,t[100100],p[100100];
stack<node>s;
set<ll>st;
map<ll,ll>mp;
char ch[5];
ll read()
{ll aa=0,bb=1;char cc=getchar();while(cc>'9'||cc<'0'){if(cc=='-') bb=-1;cc=getchar();}while(cc>='0'&&cc<='9'){aa=(aa<<3)+(aa<<1)+(cc^'0');cc=getchar();}return aa*bb;
}
bool cmp1(node a,node b)
{return a.x<b.x;
}
bool cmp2(node a,node b)
{return a.id<b.id;
}
int main()
{//freopen("test.in","r",stdin);//freopen("4.out","w",stdout);n=read();Q=read();for(int i=1;i<=n;i++){h[i].x=read();h[i].id=i;st.insert(h[i].x);}ll num=0;while(st.size()){mp[*st.begin()]=++num;p[num]=*st.begin();st.erase(*st.begin());}sort(h+1,h+n+1,cmp1);for(int i=1;i<=n;i++) h[i].x=mp[h[i].x];sort(h+1,h+n+1,cmp2);for(int i=1;i<=n;i++){ll x=h[i].x;while(s.size()&&s.top().x<=x) s.pop();if(s.size()) h[i].l=s.top().id+1;else h[i].l=1;s.push(h[i]);}while(s.size()) s.pop();for(int i=n;i>=1;i--){ll x=h[i].x;while(s.size()&&s.top().x<x) s.pop();if(s.size()) h[i].r=s.top().id;else h[i].r=n+1;s.push(h[i]);}sort(h+1,h+n+1,cmp1);for(int i=1;i<=n;i++){t[h[i].x]=t[h[i-1].x]+(h[i].id-h[i].l+1)*(h[i].r-h[i].id);}ll x;for(int i=1;i<=Q;i++){scanf("%s",ch);x=read();ll pos=lower_bound(p+1,p+num+1,x)-p;if(ch[0]=='>'){if(p[pos]==x) printf("%lld\n",t[num]-t[pos]);else printf("%lld\n",t[num]-t[pos-1]);}if(ch[0]=='='){if(p[pos]==x) printf("%lld\n",t[pos]-t[pos-1]);else puts("0");}if(ch[0]=='<'){if(p[pos]==x) printf("%lld\n",t[pos-1]);else printf("%lld\n",t[pos-1]);}}return 0;
}

#include<iostream>
#include<cstdio>
#define mod 1000000007
#define ll long long
using namespace std;
ll n,ans,f[100100];
ll quick(ll x,ll p)
{ll as=1;while(p){if(p&1) as=as*x%mod;x=x*x%mod;p>>=1;}return as;
}
int main()
{scanf("%lld",&n);ll sum=1,tot=1;for(ll i=1;i<=n;i++){f[i]=(f[i-1]*i%mod+(tot-1)*sum%mod)%mod;tot=tot*2%mod;sum=sum*i%mod;}printf("%lld\n",f[n]*quick(sum,mod-2)%mod);return 0;
}