按照
#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn=4010;
const double oo=1e16;
struct game
{
double x,y,z;
bool operator < (const game &g) const
{
return y<g.y;
}
}a[maxn];
double dp[maxn][maxn];
int n,m;
int main()
{
//freopen("c.in","r",stdin);
scanf("%d%d",&n,&m);
m-=n;
for (int i=1;i<=n;i++) scanf("%lf%lf",&a[i].x,&a[i].y);
sort(a+1,a+n+1);
for (int i=0;i<m;i++) dp[n][i]=oo;
for (int i=n-1;i>=0;i--)
{
for (int j=0;j<m;j++)
dp[i][j]=min(
1000/(a[i+1].x+a[i+1].y)+a[i+1].x/(a[i+1].x+a[i+1].y)*dp[i+1][j]+a[i+1].y/(a[i+1].x+a[i+1].y)*dp[i+1][j+1],
1000/a[i+1].y+dp[i+1][j+1]);
dp[i][m]=1000/(a[i+1].x+a[i+1].y)+dp[i+1][m];
}
printf("%.8f\n",dp[0][0]);
}