351A - Jeff and Rounding - CodeForces Solution

#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
    int n;cin>>n;
    int a[2*n];
    int cnt=0;
    double ans=1e18, sum=-n;
    for(int i=0;i<2*n;i++){
        double b;cin>>b;
        int p=(int)b;
        if(b-p==0)cnt++;
        sum+=b-p;
    }
    for(int i=0;i<=min(cnt, n);i++){
        ans=min(abs(sum+i), ans);
    }
    cout<<fixed<<setprecision(3)<<ans<<endl;

}