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55 lines
1.4 KiB
C++
55 lines
1.4 KiB
C++
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#include <iostream>
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#include <algorithm>
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#include <cmath>
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using std::cin;
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using std::cout;
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const char endl = '\n';
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long long x, a, d, n;
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int main() {
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std::ios::sync_with_stdio(false);
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cin.tie(nullptr);
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cin >> x >> a >> d >> n;
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if (d > 0) {
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if (x <= a) {
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cout << std::abs(a - x) << endl;
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} else if (x >= a + (n - 1) * d) {
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cout << std::abs(x - a - (n - 1) * d) << endl;
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} else {
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long long k = (x - a) / d;
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cout << std::min({
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std::abs(a + k * d - x),
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std::abs(a + (k - 1) * d - x),
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std::abs(a + (k + 1) * d - x),
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std::abs(a + (k - 2) * d - x),
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std::abs(a + (k + 2) * d - x),
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})
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<< endl;
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}
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} else {
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if (x >= a) {
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cout << std::abs(x - a) << endl;
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} else if (x <= a + (n - 1) * d) {
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cout << std::abs(a + (n - 1) * d - x) << endl;
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} else {
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long long k = (x - a) / d;
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cout << std::min({
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std::abs(a + k * d - x),
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std::abs(a + (k - 1) * d - x),
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std::abs(a + (k + 1) * d - x),
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std::abs(a + (k - 2) * d - x),
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std::abs(a + (k + 2) * d - x),
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})
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<< endl;
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}
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}
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return 0;
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}
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