Go: package main

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

func main() {
	io := NewIo()
	defer io.Flush()
	a, b, c := io.NextInt(), io.NextInt(), io.NextInt()
	for i := 0; i < 61; i++ {
		for j := 0; j < 61; j++ {
			if (a+b)*i-60*j <= c && c <= (a+b)*i-60*j+a {
				io.Println(60*j + c)
				return
			}
		}
	}
	io.Println(-1)
}

// I/O template
type Io struct {
	reader    *bufio.Reader
	writer    *bufio.Writer
	tokens    []string
	nextToken int
}

func NewIo() *Io {
	return &Io{
		reader: bufio.NewReader(os.Stdin),
		writer: bufio.NewWriter(os.Stdout),
	}
}

func (io *Io) Flush() {
	err := io.writer.Flush()
	if err != nil {
		panic(err)
	}
}

func (io *Io) NextLine() string {
	var buff []byte
	for {
		line, isPrefix, err := io.reader.ReadLine()
		if err != nil {
			panic(err)
		}
		buff = append(buff, line...)
		if !isPrefix {
			break
		}
	}
	return string(buff)
}

func (io *Io) Next() string {
	for io.nextToken >= len(io.tokens) {
		line := io.NextLine()
		io.tokens = strings.Fields(line)
		io.nextToken = 0
	}
	s := io.tokens[io.nextToken]
	io.nextToken++
	return s
}

func (io *Io) NextInt() int {
	i, err := strconv.Atoi(io.Next())
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) NextFloat() float64 {
	i, err := strconv.ParseFloat(io.Next(), 64)
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) Println(a ...interface{}) {
	fmt.Fprintln(io.writer, a...)
}

func (io *Io) Printf(format string, a ...interface{}) {
	fmt.Fprintf(io.writer, format, a...)
}

func (io *Io) PrintIntSlice(a []int) {
	b := make([]interface{}, 0, len(a))
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func (io *Io) PrintStringSlice(a []string) {
	b := make([]interface{}, 0, len(a))
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func Log(name string, value interface{}) {
	fmt.Fprintf(os.Stderr, "%s=%+v\n", name, value)
}

func ExampleIo() {
	io := NewIo()
	defer io.Flush()
	a := make([]int, 0, 3)
	a[0], a[1], a[2] = io.NextInt(), io.NextInt(), io.NextInt()
	io.Println(a)
	io.PrintIntSlice(a)
	Log("io", a)
}

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

int main() {
	int a,b,c;
	cin>>a>>b>>c;
	int x=c;
	if(x<=a){
		cout<<c<<endl;
		return 0;
	}
	int t=0;
	while(1){
		x=x-a;
		if(x<=0){
			cout<<(c+60*t)<<endl;
			return 0;
		}
		if(x<b){
			x=x+60-b;
			if(x==c){
				x=-1;
				cout<<x<<endl;
				return 0;
			}
		}else{
			x=x-b;
			if(x<=0){
			cout<<(c+60*t)<<endl;
			return 0;
		}
			
		}
		t++;
	}
	return 0;
}

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

int main(){

	  int a,b,c ;
	  cin >> a >> b >> c;

	  int x=c;
	  set<int> s;
	  while( c % (a+b) > a ) {
			c = c%(a+b);
			c += 60; 
			if( s.count(c) != 0){
				  cout << -1 << endl; return 0;
			}
			s.insert(c);
	  }
	  cout << x+(60*s.size()) << endl;
	  return 0;

}

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

int main() {
	int a, b, c;
	bool f[60] = {};
	cin >> a >> b >> c;
	for (int t = c; ; t += 60) {
		int d = t % (a + b);
		if (d <= a) {
			cout << t << endl;
			break;
		} else if (f[d]) {
			cout << -1 << endl;
			break;
		}
		f[d] = true;
	}
	return 0;
}

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

using namespace std;

int main(void){
  int a,b,c;
  cin >> a >> b >> c;

  for(int i=0;;i+=a+b){
    if(i<=c && c<=i+a){
      cout << i+c%60-i%60 << endl;
      break;
    }
    if(100000<i){
      cout << -1 << endl;
      break;
    }
    if(i%60 != (i+a)%60)c+=60;
  }
  
  return 0;
}

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

using namespace std;

void solve(int a,int b,int c) {
    int t = 0;
    for(int i=0; ; i+=a+b) {
        c += 60 * (i / 60);
        if(i<=c and c<=i+a) {
            cout << c << "\n";
            return ;
        }
        if(t > 1e5) break;
    }
    cout << -1 << "\n";
}

int main() {
    int a,b,c; cin>>a>>b>>c;
    solve(a,b,c);
    return 0;
}

C++: //#define USE_CPP11
// #define USE_PRINTF

#include <iostream>
#include <iomanip>
#include <map>
#include <set>
#include <utility>
#include <vector>
#include <string>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <list>
#include <queue>
#include <deque>
#include <stack>
#include <numeric>
#include <complex>
#include <memory>
#include <sstream>

#ifdef USE_CPP11
#include <unordered_map>
#include <unordered_set>
#include <functional>
#endif

#define PRINT(obj) cout << obj << endl
#define REP(i, n) for(int (i) = 0; (i) < (n); i++)
#define SPACE " "

typedef long long ll;

const int INF = 1e9 + 10;

using namespace std;

namespace Scanner {
#ifdef USE_PRINTF
  int    nextInt()    { int    d; scanf("%d" , &d); return d; }
  float  nextFloat()  { float  f; scanf("%f" , &f); return f; }
  double nextDouble() { double f; scanf("%lf", &f); return f; }  
  string nextString() { string s; scanf("%s" , &s); return s; }
  ll     nextll()     { ll     l; scanf("%ll", &l); return l; }
#else
  int    nextInt()    { int    d; cin >> d; return d; }
  float  nextFloat()  { float  f; cin >> f; return f; }
  double nextDouble() { double f; cin >> f; return f; }  
  string nextString() { string s; cin >> s; return s; }
  ll     nextll()     { ll     l; cin >> l; return l; }
#endif

  string getLine() { 
    string input;
    getline(cin, input);
    return input;
  }
};

namespace myLibrary {
  vector<string> split(const string& str, char delim) {
    vector<string> ret;
    size_t current = 0, found;
    while ((found = str.find_first_of(delim, current)) != string::npos) {
      ret.push_back(string(str, current, found - current));
      current = found + 1;
    }
    ret.push_back(string(str, current, str.size() - current));
    return ret;
  }
  
#ifdef USE_CPP11
  ///
  /// higher-order functional
  /// This is something like map in haskell, python, etc.
  /// Sample usage:
  ///   vector<int> a = {1, 2, 3, 4, 5};
  ///   vector<int> b = myLibrary::_Map<int, int>(a, [](int n){
  ///     return n * n;
  ///   });
  /// Result:
  ///   b = 1, 4, 9, 16, 25
  ///
  template<typename T_IN, typename T_OUT, class Functor>
  vector<T_OUT> _Map(vector<T_IN> src, Functor func) {
    vector<T_OUT> ret;
    for (int i = 0; i < src.size(); i++) {
      ret.push_back(func(src[i]));
    }
    return ret;
  }
#endif

};

/// BEGIN //////////////////////////////////////////////////////////

int main() {
  int a = Scanner::nextInt();
  int b = Scanner::nextInt();
  int c = Scanner::nextInt();

  for (int t = 0; ; t++) {
    int m = 60 * t + c;
    if (m < 0) {
      PRINT(-1);
      break;
    }
    int n = m % (a + b);
    if (n <= a) {
      PRINT(m);
      break;
    }
  }

  return 0;
}
/// END   //////////////////////////////////////////////////////////

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

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll, ll> P;

#define EACH(i,a) for (auto& i : a)
#define FOR(i,a,b) for (ll i=(a);i<(b);i++)
#define RFOR(i,a,b) for (ll i=(b)-1;i>=(a);i--)
#define REP(i,n) for (ll i=0;i<(n);i++)
#define RREP(i,n) for (ll i=(n)-1;i>=0;i--)
#define debug(x) cout<<#x<<": "<<x<<endl
#define pb push_back
#define ALL(a) (a).begin(),(a).end()

const ll linf = 1e18;
const int inf = 1e9;
const double eps = 1e-12;
const double pi = acos(-1);

template<typename T>
istream& operator>>(istream& is, vector<T>& vec) {
	EACH(x,vec) is >> x;
	return is;
}
template<typename T>
ostream& operator<<(ostream& os, vector<T>& vec) {
	REP(i,vec.size()) {
		if (i) os << " ";
		os << vec[i];
	}
	return os;
}
template<typename T>
ostream& operator<<(ostream& os, vector< vector<T> >& vec) {
	REP(i,vec.size()) {
		if (i) os << endl;
		os << vec[i];
	}
	return os;
}

int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(0);
	int a, b, c; cin >> a >> b >> c;
	int T = a + b;
	REP(t, 1000) {
		ll t0 = 60 * t + c;
		ll k = t0 / T;
		ll l = k * T, r = k * T + a;
		if (l <= t0 && t0 <= r) {
			cout << t0 << endl;
			return 0;
		}
	}
	cout << -1 << endl;
}