直接判。

#include<bits/stdc++.h>
//#define int long long
#define INF 0x3f3f3f
using namespace std;
double n;
signed main(){
	cin>>n;
	if(n!=int(n))n=int(n)+1;
	if(n<=5)cout<<"10";
	else cout<<(n-5)*3+10;
	return 0;
}

C++ :

#include<bits/stdc++.h>
using namespace std;
float n;
int main(){
	cin>>n;
	if(n!=int(n)) n=int(n+1);
	if(n<=5) cout<<10;
	else cout<<10+(n-5)*3;
	return 0;
}

Python :

# coding=utf-8
i=float(input())
if (i<=5):
    print(10)
else:
    if (i==int(i)):
        i=int(i)
    else:
        i=int(i+1)
    s=10+(i-5)*3
    print(s)