Go: package main

import "fmt"

func main() {
	var F int
	fmt.Scan(&F)
	fmt.Println((F - 30)/2)
}

C++: #include "bits/stdc++.h"
#pragma GCC optimize("Ofast")

// Begin Header {{{
using namespace std;

#ifndef DEBUG
#define dump(...)
#endif

#define all(x) x.begin(), x.end()
#define rep(i, b, e) for (intmax_t i = (b), i##_limit = (e); i < i##_limit; ++i)
#define reps(i, b, e) for (intmax_t i = (b), i##_limit = (e); i <= i##_limit; ++i)
#define repr(i, b, e) for (intmax_t i = (b), i##_limit = (e); i >= i##_limit; --i)
#define var(Type, ...) Type __VA_ARGS__; input(__VA_ARGS__)

constexpr size_t    operator""_zu(unsigned long long value) { return value; };
constexpr intmax_t  operator""_jd(unsigned long long value) { return value; };
constexpr uintmax_t operator""_ju(unsigned long long value) { return value; };

constexpr int INF = 0x3f3f3f3f;
constexpr intmax_t LINF = 0x3f3f3f3f3f3f3f3f_jd;

template <class T, class Compare = less<>>
using MaxHeap = priority_queue<T, vector<T>, Compare>;
template <class T, class Compare = greater<>>
using MinHeap = priority_queue<T, vector<T>, Compare>;

inline void input() {}
template <class Head, class... Tail>
inline void input(Head&& head, Tail&&... tail) {
    cin >> head;
    input(forward<Tail>(tail)...);
}

template <class T>
inline istream& operator>>(istream &is, vector<T> &vec) {
    for (auto &e: vec) {
        is >> e;
    }
    return is;
}

inline void output() { cout << "\n"; }
template <class Head, class... Tail>
inline void output(Head&& head, Tail&&... tail) {
    cout << head;
    if (sizeof...(tail)) {
        cout << " ";
    }
    output(forward<Tail>(tail)...);
}

template <class T>
inline ostream& operator<<(ostream &os, const vector<T> &vec) {
    static constexpr const char *delim[] = {" ", ""};
    for (const auto &e: vec) {
        os << e << delim[&e == &vec.back()];
    }
    return os;
}

template <class T>
inline vector<T> makeVector(const T &initValue, size_t sz) {
    return vector<T>(sz, initValue);
}

template <class T, class... Args>
inline auto makeVector(const T &initValue, size_t sz, Args... args) {
    return vector<decltype(makeVector<T>(initValue, args...))>(sz, makeVector<T>(initValue, args...));
}

template <class Func>
class FixPoint : Func {
public:
    explicit constexpr FixPoint(Func&& f) noexcept : Func(forward<Func>(f)) {}

    template <class... Args>
    constexpr decltype(auto) operator()(Args&&... args) const {
        return Func::operator()(*this, std::forward<Args>(args)...);
    }
};

template <class Func>
static inline constexpr decltype(auto) makeFixPoint(Func&& f) noexcept {
    return FixPoint<Func>{forward<Func>(f)};
}

template <class Container>
struct reverse_t {
    Container &c;
    reverse_t(Container &c) : c(c) {}
    auto begin() { return c.rbegin(); }
    auto end() { return c.rend(); }
};

template <class Container>
auto reversed(Container &c) {
    return reverse_t<Container>(c);
}

template <class T>
inline bool chmax(T &a, const T &b) noexcept {
    return b > a && (a = b, true);
}

template <class T>
inline bool chmin(T &a, const T &b) noexcept {
    return b < a && (a = b, true);
}

template <class T>
inline T diff(const T &a, const T &b) noexcept {
    return a < b ? b - a : a - b;
}
// End Header }}}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.setf(ios_base::fixed);
    cout.precision(10);

    var(intmax_t, F);
    output((F - 30) / 2);

    return 0;
}

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

return 0;
}

C++: #include <cstdio>
using namespace std;
int main() {
    int F;
    scanf("%d", &F);
    printf("%d\n", (F-30)/2);
    return 0;
}

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

int main (){

    int F;
    cin >> F;

    cout << (F-30)/2 << endl;

    return 0;

}

C++: #include <iostream>
using namespace std;
int main(void){
    
    int c,f;
    cin>>f;
    
    c=(f-30)/2;
    
    cout<<c<<endl;
}

C++: #include <bits/stdc++.h>
using namespace std;

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

  return 0;
}

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

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

int main()
{
	int f;

	cin >> f;

	cout << (f - 30) / 2 << endl;

	return 0;
}

C++: // Celcius and Fahrenheit 2018/12/28

#include <iostream>
using namespace std;

int main() {
    int F, C;
    cin >> F;
    cout << (F - 30) / 2 << '\n';
    return 0;
}

~

C++: #include <bits/stdc++.h>
using namespace std;

int main(){
    int F;
    cin >> F;
    int C = ( F - 30 ) / 2;
    cout << C <<endl;
    return 0;
    // Your code here!
    
}

C++: #include <bits/stdc++.h>
 
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,n) for(int i=1;i<=(n);i++)
#define lol long long
#define SUM(n) ((n)+1)*(n)/2 //1〜nまでの総和を求める式
#define mp make_pair
#define fi first
#define se second
#define pu push_back
#define SYOU(x) fixed<<setprecision(x+1) //小数点桁数を指定する
#define abs(x,y) max(x,y)-min(x,y)
#define all(v) v.begin(),v.end()
#define UPDigit(a,b) (a+b-1)/b //小数点切り上げ
const int INF = 0x3f3f3f3f;
const long long LINF = 0x3f3f3f3f3f3f3f3fLL;
const int MOD=int(1e9)+7; 
using namespace std;
using pii = pair<lol, lol>;
typedef vector<int> vit;

//最大公約数
lol gcd(lol x, lol y){
  if(x < y) swap(x, y);
  lol r = x % y;
  while(r != 0){
    x = y;
    y = r;
    r = x % y;
  }
  return y;
}
//最小公倍数
lol lcm(lol x, lol y){
  lol a = x * y;
  return (a / gcd(x, y));
}

signed main(void){
  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
  int f;
  cin >> f;
  cout << (f - 30) / 2 << '\n';
  return 0;
}

C++: #include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<iomanip>
#include<math.h>
#include<complex>
#include<queue>
#include<deque>
#include<stack>
#include<map>
#include<set>
#include<bitset>
#include<functional>
#include<assert.h>
#include<numeric>
#include<stdio.h>
#include <cstdint>
using namespace std;
#define REP(i,m,n) for(int i=(int)(m) ; i < (int) (n) ; ++i )
#define rep(i,n) REP(i,0,n)
using ll = long long;
const int inf = 1e9 + 7;
const ll longinf = 1LL << 60;
const ll mod = 1e9 + 7;

int F;

int main() {

	cin >> F;
	cout << (F - 30) / 2 << endl;

	return 0;
}

C++: #include<bits/stdc++.h>
#define V vector
#define VI vector<int>
#define VVI vector<vector<int>>
#define FOR(n) for(int i=0;i<n;i++)
#define MOD 1e9+7
#define INF 1e9
#define F first
#define S second
#define ALL(x) (x).begin(),(x).end()
using namespace std;
typedef long long ll;
int main(void){
  int n;
  cin>>n;
  int ans=n/2-15;
  cout<<ans<<endl;
  return 0;
}

C++: #define rep(i, n) for (int i = 0; i < (int)(n); i++)
typedef long long ll;
 
#include <bits/stdc++.h>
using namespace std;
 
int main(){
  int f;
  cin>>f;
  
  cout<<(f-30)/2<<endl;
      
  return 0;
}

C++: #include<iostream>

using namespace std;
int main(){
    int f;

    cin >> f;
    cout << (f - 30) / 2 << endl;
}

C++: #include<stdio.h>
int main(){
	int c,f;
	scanf("%d",&f);
	c=(f-30)/2;
	printf("%d\n",c);
	return 0;
}

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

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

  cout << (F-30)/2 << endl;

  return 0;
}

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

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

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

using namespace std;

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

  return 0;
}

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;


}