题目地址


#include<cstdio>
#include<iostream>
#define ll long long
using namespace std;

void exgcd(ll a,ll b,ll &x,ll &y){
	if(!b){
		x=1,y=0;
		return;
	}
	exgcd(b,a%b,x,y);
	ll tmp=x;
	x=y,y=tmp-(a/b)*y;
}

int main(){
	ll a,b;
	scanf("%lld%lld",&a,&b);
	ll x,y;
	exgcd(a,b,x,y);
	printf("%lld\n",(x+b)%b);
	return 0;
}