#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
struct Point;
typedef Point Vector;
struct Point {
ll x,y;
Point(){}
Point(ll _x,ll _y):x(_x),y(_y){}
ll how_many_points(Point p){
int g=__gcd(abs(x-p.x),abs(y-p.y));
return g+1;
}
Vector operator-(Vector v){
return Vector(x-v.x,y-v.y);
}
ll cross(Vector p){
return x*p.y-y*p.x;
}
};
ll n,m,p;
int main() {
scanf("%lld%lld%lld",&n,&m,&p);
Point O(0,0);
Point A(n,m);
Point B(p,0);
Vector _A=(A-O);
Vector _B=(B-O);
ll _2S=abs(_A.cross(_B));
ll b=(O.how_many_points(A)+A.how_many_points(B)+B.how_many_points(O))-3;
ll _2a=_2S-b+2;
printf("%lld\n",_2a/2ll);
}