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// Laufzeit: O(log(b))
ll mult_mod(ll a, ll b, ll n) {
if(a == 0 || b == 0) return 0;
if(b == 1) return a % n;
if(b % 2 == 1) return (a + mult_mod(a, b-1, n)) % n;
else return mult_mod((a + a) % n, b / 2, n);
}
// Laufzeit: O(log(b))
ll pow_mod(ll a, ll b, ll n) {
if(b == 0) return 1;
if(b == 1) return a % n;
if(b % 2 == 1) return mult_mod(pow_mod(a, b-1, n), a, n);
else return pow_mod(mult_mod(a, a, n), b / 2, n);
}
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