Go: package main

import "fmt"

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

C++: //↓template↓

#include "bits/stdc++.h"
using namespace std;
#define Would
#define you
#define all(n)  n.begin(),n.end()
#define rall(n) n.rbegin(),n.rend()
typedef long long ll;
const ll INF = 1e18;
const ll MOD = 1e9 + 7;
const double EPS = 1e-10;
const double pi = acos(-1);//3.1415926535897932384626433832795028...
const ll SIZE = 1 << 17;
int dx[] = { 1,0,-1,0 }, dy[] = { 0,1,0,-1 }, alp[30];
ll fac[200005], finv[200005], inv[200005];
vector<ll>dij;
struct edge { ll to, cost; };
vector<vector<edge> >G;

ll mod_pow(ll a, ll b) {
	ll res = 1, mul = a;
	for (int i = 0; i < 31; ++i) {
		if (b >> i & 1) {
			res *= mul;
			res %= MOD;
		}
		mul = (mul * mul) % MOD;
	}
	return res;
}

void addedge(int from, int to, int cost) {
	G[from].push_back({ to,cost });
	G[to].push_back({ from,cost });
}

template<typename T>
vector<T> make_v(size_t a) { return vector<T>(a); }

template<typename T, typename... Ts>
auto make_v(size_t a, Ts... ts) {
	return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

template<typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type
fill_v(T & t, const V & v) { t = v; }

template<typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type
fill_v(T & t, const V & v) {
	for (auto& e : t) fill_v(e, v);
}

template<typename T>
void outp(vector<T>v) {
	for (int i = 0; i < v.size(); ++i) {
		cout << v[i];
		if (i != v.size() - 1) { cout << " "; }
	}
}

double add(double a, double b) {
	if (abs(a + b) < EPS * (abs(a) + abs(b))) { return 0; }
	return a + b;
}


//↑template↑


int main() {

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



}

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

using namespace std;


signed main(){

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

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

C++: #include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll INF = 1e16;
const ll mod = 1000000007;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

template<class T> inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template<class T> inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
int ctoi(char c) {
  if (c >= '0' && c <= '9') {
    return c - '0';
  }
  return 0;
}
ll factorial(ll n) {
  if (n == 1) {
    return 1;
  }
  ll ans = factorial(n-1);
  return ans*n;
}
ll gcd(ll a, ll b) {
  if (b == 0) return a;
  return gcd(b, a%b);
}
ll lcm(ll a, ll b) {
  return (a/gcd(a, b))*b;
}
bool is_prime(ll n) {
  for (ll i = 2; i*i <= n; i++) {
    if (n%i == 0) return false;
  }
  return n != 1;
}
ll mod_pow(ll x, ll n, ll mod) {
  if (n == 0) return 1;
  ll res = mod_pow(x*x%mod, n/2, mod);
  if (n & 1) res = res * x % mod;
  return res;
}

int main() {
    ll n;
    cin >> n;
    cout << (n-30)/2 << endl;
}

C++: #pragma GCC target("sse,sse2,sse3,sse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize("Ofast")

#include <bits/stdc++.h>

using namespace std;

using ll = long long;

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

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

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

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

using namespace std;

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

return 0;
}

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

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

int main() {
  int f;
  cin >> f;
  cout << (f - 30) / 2 << "\n";
}

C++: #include <bits/stdc++.h>
using namespace std;
int main(){
  long long 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 << "\n";
	
	return 0;

}

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

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

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

C++: /*
　　　　 ∧＿∧　にっぽんちゃちゃちゃ
　／＼（　・∀・）／ヽ
（ ●　と　　　つ　● ）　にっぽんちゃちゃちゃ
　＼/⊂、 ノ　　＼ノ
　　　　　し'
*/
#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<(int)(n);++i)
#define repone(i,n) for(int i=1;i<(int)(n);++i)
#define repo(i,o,n) for(int i=o;i<(int)(n);++i)
#define Rep(j,n) for(int j=0;j<(int)(n);++j)
#define Repo(j,o,n) for(int j=o;j<(int)(n);++j)
#define Repone(j,n) for(int j=1;j<(int)(n);++j)
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define int long long
#define MOD 1000000007
#define INF 9223372036854775807

signed main()
{
int x=0,y=0,z=0,w=0,n=0,d=0;
std::cin >> x;
std::cout << (x-30)/2 << '\n';
}

C++: #include<iostream>
#include<iomanip>
#include<math.h>
#include<algorithm>
#include<functional>
#include<utility>
#include<queue>
#include<string.h>
#include<string>
#include<set>
#include<map>
#include<vector>
using namespace std;
typedef long long LL;
typedef pair<int, int> P;
LL N,M;

int main(){
    cin>>N;

    cout<<(N-30)/2<<endl;
    return 0;
}

C++: #include <iostream>
#include <stdio.h>
#include <math.h>
#include <algorithm>
using namespace std;
int main(){
  int a;
  cin >> a;
  cout << (a-30)/2 << endl;
}

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

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

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

C++: # include "bits/stdc++.h"
using namespace std;
using LL = long long;
using ULL = unsigned long long;
const double PI = acos(-1);
template<class T>constexpr T INF() { return ::std::numeric_limits<T>::max(); }
template<class T>constexpr T HINF() { return INF<T>() / 2; }
template <typename T_char>T_char TL(T_char cX) { return tolower(cX); };
template <typename T_char>T_char TU(T_char cX) { return toupper(cX); };
typedef pair<LL, LL> pii;
const int vy[] = { -1, -1, -1, 0, 1, 1, 1, 0 }, vx[] = { -1, 0, 1, 1, 1, 0, -1, -1 };
const int dx[4] = { 0,1,0,-1 }, dy[4] = { 1,0,-1,0 };
int popcnt(unsigned long long n) { int cnt = 0; for (int i = 0; i < 64; i++)if ((n >> i) & 1)cnt++; return cnt; }
int d_sum(LL n) { int ret = 0; while (n > 0) { ret += n % 10; n /= 10; }return ret; }
int d_cnt(LL n) { int ret = 0; while (n > 0) { ret++; n /= 10; }return ret; }
LL gcd(LL a, LL b) { if (b == 0)return a; return gcd(b, a%b); };
LL lcm(LL a, LL b) { LL g = gcd(a, b); return a / g*b; };
# define ALL(qpqpq)           (qpqpq).begin(),(qpqpq).end()
# define UNIQUE(wpwpw)        sort(ALL((wpwpw)));(wpwpw).erase(unique(ALL((wpwpw))),(wpwpw).end())
# define LOWER(epepe)         transform(ALL((epepe)),(epepe).begin(),TL<char>)
# define UPPER(rprpr)         transform(ALL((rprpr)),(rprpr).begin(),TU<char>)
# define FOR(i,tptpt,ypypy)   for(LL i=(tptpt);i<(ypypy);i++)
# define REP(i,upupu)         FOR(i,0,upupu)
# define INIT                 std::ios::sync_with_stdio(false);std::cin.tie(0)

int f;

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

C++: #include <bits/stdc++.h>
using namespace std;
int main(){
    int a;
    cin>>a;
    cout<<(a-30)/2<<endl;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
    int F;
    cin >> F;
    cout << (F - 30) / 2 << "\n";
    return 0;
}

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

C++: #include <iostream>
using namespace std;
int main(void){
    // Your code here!
    int x;
    cin>>x;
    cout<<(x-30)/2<<endl;
}