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Cod sursa(job #846186)
#include<cstdio>
using namespace std;
int a,n,e=1,d,inv=1,i,N;
int main()
{
freopen("inversmodular.in","r",stdin);
freopen("inversmodular.out","w",stdout);
scanf("%lld%lld",&a,&n);
N=n;
if(!(n%2))
{
while(!(n%2)) {n/=2;e*=2;}
e/=2;
}
for(d=3;d*d<=n;d+=2)
{
if(!(n%d))
{
while(!(n%d)) {n/=d;e*=d;}
e/=d;e*=d-1;
}
}
if(n>1) e*=n-1;
e--;
for(i=1;i<=e;i<<=1)
{
if(i&e) inv=(inv*a)%N;
a=(a*a)%N;
}
printf("%lld\n",inv);
return 0;
}