//#define _GLIBCXX_DEBUG #include <bits/stdc++.h> #define int long long #define ld long double using namespace std; const int INF = 1e18; const int mod = 1e9+7; const int N = 101; pair<ld,int> dp[N][N][N]; signed main() { int n,k; cin >> n >> k; vector <pair<int,int>> vec(n); for (int i = 0;i < n;i++) { cin >> vec[i].first >> vec[i].second; } for (int i = 0;i < N;i++) { for (int j = 0;j < N;j++) { for (int z = 0;z < N;z++) { dp[i][j][z] = {INF,INF}; } } } for (int i = 0;i < n;i++) { dp[i][0][0] = {0,0}; dp[i][1][0] = {vec[i].first,vec[i].first}; if (vec[i].second != -1)dp[i][0][1] = {vec[i].second,0}; } for (int i = 0;i < n - 1;i++) { for (int j = 0;j <= n;j++) { for (int z = 0;z <= n;z++) { //dp[i][j][z] if (j != n) { pair<ld,int> res = dp[i][j][z]; res.first -= (res.second / (1.0l * (z + 1))); res.second += vec[i+1].first; res.first += (res.second / (1.0l * (z + 1))); if (dp[i+1][j+1][z].first > res.first) { dp[i+1][j+1][z] = res; }else if (dp[i+1][j+1][z].first == res.first) { dp[i+1][j+1][z].second = max(dp[i+1][j+1][z].second,res.second); } } if (dp[i+1][j][z].first > dp[i][j][z].first) { dp[i+1][j][z] = dp[i][j][z]; }else if (dp[i+1][j][z].first == dp[i][j][z].first) { dp[i+1][j][z].second = max(dp[i+1][j][z].second,dp[i][j][z].second); } if (z != n && vec[i+1].second != -1) { pair<ld,int> res = dp[i][j][z]; res.first -= (res.second / (1.0l * (z + 1))); res.first += (vec[i+1].second / (1.0l * (z + 1))); res.first += (res.second / (1.0l * (z + 2))); if (dp[i+1][j][z+1].first > res.first) { dp[i+1][j][z+1] = res; }else if (dp[i+1][j][z+1].first == res.first) { dp[i+1][j][z+1].second = max(dp[i+1][j][z+1].second,res.second); } } } } } ld best = INF; for (int i = 0;i <= k;i++) { best = min(best,dp[n-1][i][k-i].first); } cout << best << "\n"; }