C++ :

#include<iostream>
using namespace std;
int main(){
	float s;
	float vc,vd,vm;
	cin>>s>>vc>>vd>>vm;
	int sum=0;
	while(s>0.8){
		if(sum%2==0){//从c->d
		 	s-=s/(vd+vm)*(vc+vd);
			sum++;
		}
		else{ //从 d->c 
			s-=s/(vc+vm)*(vc+vd);
			sum++;
		}
	}
	cout<<sum<<endl;
	
	return 0;
} 

Pascal :

var
  k:integer;
  s,vc,vd,vm,t:real;
begin
  readln(s);
  readln(vc);
  readln(vd);
  readln(vm);
  while s>0.8 do
    begin
      inc(k);
      if odd(k) then
        t:=s/(vd+vm)
        else 
        t:=s/(vc+vm);
      s:=s-(vc+vd)*t;
    end;
  write(k);
end.