#include<iostream>
#include<cstdio>
#include<string>
#include<algorithm>
#include<queue>
#include<list>
#include<cstring>
#include<cassert>
using namespace std;
int n, m, p;
int gcd(int x, int y){
    if (x == 0)return y;
    return gcd(y%x, x);
}
int main(){
    ios::sync_with_stdio(false);
    cin >> n >> m >> p;
    int e = gcd(n, m) + gcd(abs(p - n), m) + p;
    printf("%d", p*m/2 + 1 - e / 2);
}