[P1984][SDOI2008]烧水问题

#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<queue>
#include<vector>
#include<climits>
#include<string>
#include<cstdlib>
#include<ctime>
#define LL long long
#define MOD 1000000007
#define pi 3.141592653589
using namespace std;

int n,i;
double v,s,t1,t2,ans;

int main()
{
scanf("%d",&n);

v=1.0/n;
s=4200*v;

t1=1.0*100;
ans+=t1;

for(i=2;i<=n;i++)
{
t2=t1*(1.0-(1.0/(2*(i-1))));
ans+=t2;
t1=t2;
}

ans=s*ans;
printf("%.2lf",ans);

return 0;
}