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Cod sursa(job #228198)
#include <stdio.h>
#include <assert.h>
#define ll long long
int A, N;
void gcd(ll &x, ll &y, int &d, int a, int b)
{
if (!b)
d = a, x = 1, y = 0;
else
{
gcd(x, y, d, b, a % b);
ll aux = x;
x = y;
y = aux - y * (a / b);
}
}
int main()
{
ll inv = 0, ins;
int d;
freopen("inversmodular.in", "r", stdin);
freopen("inversmodular.out", "w", stdout);
scanf("%d %d", &A, &N);
assert(1 <= A && A < N && N <= 2000000000);
gcd(inv, ins, d, A, N);
assert(d == 1);
if (inv <= 0)
inv += N - inv % N;
printf("%lld\n", inv);
return 0;
}