I think it's quite a difficult problem. WA struggled for a long time.
Some techniques need to be used, precision issues.
The initial idea is that when a fast person runs once, they will definitely collide once.
In addition to colliding directly at the endpoints, there may also be issues with different endpoints.
//
// GGGGGGGGGGGGG CCCCCCCCCCCCC AAA
// GGG::::::::::::G CCC::::::::::::C A:::A
// GG:::::::::::::::G CC:::::::::::::::C A:::::A
// G:::::GGGGGGGG::::G C:::::CCCCCCCC::::C A:::::::A
// G:::::G GGGGGG C:::::C CCCCCC A:::::::::A
//G:::::G C:::::C A:::::A:::::A
//G:::::G C:::::C A:::::A A:::::A
//G:::::G GGGGGGGGGGC:::::C A:::::A A:::::A
//G:::::G G::::::::GC:::::C A:::::A A:::::A
//G:::::G GGGGG::::GC:::::C A:::::AAAAAAAAA:::::A
//G:::::G G::::GC:::::C A:::::::::::::::::::::A
// G:::::G G::::G C:::::C CCCCCC A:::::AAAAAAAAAAAAA:::::A
// G:::::GGGGGGGG::::G C:::::CCCCCCCC::::C A:::::A A:::::A
// GG:::::::::::::::G CC:::::::::::::::C A:::::A A:::::A
// GGG::::::GGG:::G CCC::::::::::::C A:::::A A:::::A
// GGGGGG GGGG CCCCCCCCCCCCCAAAAAAA AAAAAAA
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <climits>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <cctype>
#include <utility>
#include <ctime>
using namespace std;
#ifdef DEBUG
#define debug(...) printf("!\_\_DEBUG: "),printf(\_\_VA\_ARGS\_\_)
#define gettime() end\_time=clock();printf("now running time is %.7f\\n",(float)(end\_time - start\_time)/CLOCKS\_PER\_SEC);
#else
#define debug(...)
#define gettime()
#endif
typedef unsigned int uint;
typedef long long int Int;
#define Set(a,s) memset(a,s,sizeof(a))
#define Write(w) freopen(w,"w",stdout)
#define Read(r) freopen(r,"r",stdin)
#define Pln() printf("\\n")
#define I\_de(x,n)for(int i=0;i<n;i++)printf("%d ",x\[i\]);Pln()
#define De(x)printf(#x"%d\\n",x)
#define For(i,x)for(int i=0;i<x;i++)
#define CON(x,y) x##y
#define Pmz(dp,nx,ny)for(int hty=0;hty<ny;hty++){for(int htx=0;htx<nx;htx++){\\
printf("%d ",dp\[htx\]\[hty\]);}Pln();}
#define M 55
#define PII pair<int,int\>
#define PB push\_back
#define oo INT\_MAX
#define Set\_oo 0x3f
#define FOR(it,c) for(\_\_typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define eps 1e-10
bool xdy(double x,double y){return x>y+eps;}
bool xddy(double x,double y){return x>y-eps;}
bool xcy(double x,double y){return x<y-eps;}
bool xcdy(double x,double y){return x<y+eps;}
bool xeqy(double x,double y){return fabs(x-y)<eps;}
int min3(int x,int y,int z){
int tmp=min(x,y);
return min(tmp,z);
}
int max3(int x,int y,int z){
int tmp=max(x,y);
return max(tmp,z);
}
Int l,u,v,t;
Int gcd(Int a,Int b){
if(b==0)return a;
return gcd(b,a%b);
}
void solve(){
Int g=gcd(u,v);
// debug("%lld %lld\\n",u,v);
if(v==0){
if(u==0){
puts("0");
return ;
}
Int ans=t\*u/l;
// debug("%lld\\n",ans);
printf("%lld\\n",ans/2+((ans&1)));
return ;
}
long double su=1.0\*l/u,sv=1.0\*l/v;
Int ans=(t\*u)/l;
Int ans2=(t\*v)/l;
Int fans=ans;
long double mt=1.0\*l/g;
// double r=t-ans\*su;
// double r2=t-ans2\*sv;
debug("%lld\\n",fans);
Int tm=t\*u%l;
Int tm2=t\*v%l;
tm%=l;tm2%=l;
debug("tm>>%lld %lld %lld %lld\\n",tm,tm2,ans,ans2);
if(((ans+ans2)&1)&&(tm!=0||tm2!=0)){
if(tm>=tm2)fans++;
}else{
if(tm>=l-tm2)fans++;
}
debug("%lld\\n",fans);
if((u/g-v/g)&1){
Int tmp=t/mt;
debug("tmp >>%lld %lld %f \\n",tmp,t,mt);
fans-=tmp/2;
if(xdy(t,tmp\*mt)&&(tmp&1)){
fans-=1;
}
}
// debug("%lld %.6f\\n\\n",fans,mt);
printf("%lld\\n",fans);
}
int main() {
// freopen("out.txt","w",stdout);
ios\_base::sync\_with\_stdio(0);
while(~scanf("%lld%lld%lld%lld",&l,&u,&v,&t)&&l){
if(v>u)swap(u,v);
solve();
}
// gettime();
}