#include <algorithm>
#include <array>
#include <bit>
#include <bitset>
#include <cassert>
#include <cctype>
#include <chrono>
#include <climits>
#include <clocale>
#include <cmath>
#include <complex>
#include <concepts>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <numbers>
#include <numeric>
#include <queue>
#include <random>
#include <ranges>
#include <regex>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

constexpr int MOD{1'000'000'007};
constexpr int MOD2{998'244'353};
constexpr int INF{1'000'000'000}; //1e9
constexpr int NIL{-1};
constexpr long long LINF{1'000'000'000'000'000'000}; // 1e18
constexpr long double EPS{1E-10L};
using namespace std::literals;
namespace ranges = std::ranges;
namespace views = ranges::views;

template<class T, class S> bool chmax(T &a, const S &b){
    if(a < b){a = b; return true;}
    return false;
}
template<class T, class S> bool chmin(T &a, const S &b){
    if(b < a){a = b; return true;}
    return false;
}
template<class T> bool inside(T x, T lx, T rx){ //semi-open
    return (ranges::clamp(x, lx, rx-1) == x);
}
template<class T> bool inside(T x, T y, T lx, T rx, T ly, T ry){
    return inside(x, lx, rx) && inside(y, ly, ry);
}
template<class Container> void print_contariner(Container &c, std::string sep = " "s, std::string end = "\n"s){
    for(int i{int(std::size(c))}; auto e: c) std::cout << e << (--i ? sep : end);
}



int main(){
    int A, B, C; std::cin >> A >> B >> C;
    auto f{[=](int x){
        x *= A;
        if(x >= B) x -= B;
        if(x == C) std::cout << x << "\n";
        return x == C;
    }};
    bool ex{false};
    if(!(C % A) && f(C / A)) ex = true;
    if(!((C + B) % A) && f((C + B) / A)) ex = true;
    if(!ex) std::cout << -1 << std::endl;
    return 0;
}