Go: package main

import (
	"fmt"
	"bufio"
	"os"
	"strconv"
	"strings"
)

var sc = bufio.NewScanner(os.Stdin)

func nextLine() string {
	sc.Scan()
	return sc.Text()
}

func nextLineInt() []int {
	arr := strings.Split(nextLine(), " ")
	var ret []int
	for _, v := range arr {
		x, _ := strconv.Atoi(v)
		ret = append(ret, x)
	}
	return ret
}

func main() {
	cin := nextLineInt()
	F := cin[0]
	fmt.Println((F-30)/2)
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <string>

#define INF 100000;

int main() {
  int F;
  std::cin >> F;

  std::cout << (F-30)/2 << "\n";

  return 0;
}

C++: #include<iostream>
using namespace std;

int main(){

  int f, ans;

  cin >> f;

  ans = (f - 30) / 2;

  cout << ans << endl;

  return 0;


}

C++: #include<bits/stdc++.h>
using namespace std;
using ll = long long; 
using ull = unsigned long long;
using V = vector<int>;
using VV = vector<vector<int>>;
using VVV = vector<vector<vector<int>>>;
using VL = vector<ll>;
using VVL = vector<vector<ll>>;
using VVVL = vector<vector<vector<ll>>>;
template<class T> using P = pair<T, T>;
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define REP(i,k,n) for(int i=(k);i<(n);i++)
#define all(a) (a).begin(),(a).end()
#define output(x,y) cout << fixed << setprecision(y) << x << endl;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
const ll MOD = 1e9 + 7;
// const ll MOD = 998244353;
ll upper = MOD + MOD;
ll under = -upper;
ll UPPER = MOD * MOD;
ll UNDER = -UPPER;
const long double pi = 3.141592653589793;
int main() {
	int n;
	cin >> n;
	cout << (n - 30) / 2 << endl;
	return 0;
}

C++: #include<iostream>
using namespace std;

int F,C;

int main(){
cin>>F;
C=(F-30)/2;
cout<<C<<endl;

return 0;
}

C++: #include<iostream>
using namespace std;
int main(){
    int A=0;
    cin >> A ;
    cout << (A-30)/2 << endl;
    return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

int main() {
	int f;
	cin >> f;
	cout << (f - 30) / 2 << endl;
	return 0;
}

C++: #include <stdio.h>
#include <iostream>
#include <string>

using namespace std;

int main(){
	int F;
	cin >> F;
	cout << (F - 30) / 2;
}

C++: #include<iostream>
using namespace std;
int main() {
	int num;
	cin >> num;
	cout << (num - 30) / 2 << endl;
	return 0;
}