#include<bits/stdc++.h>
#define int long long
using namespace std;
int gcd(int a,int b){return b?gcd(b,a%b):a;}
bool ok[4010000];
signed main(){
    int A,B,C;cin>>A>>B>>C;
    if(gcd(gcd(A,B),C)!=1){
        puts("-1");
        return 0;
    }
    int ans=0;
    ok[0]=1;
    for(int i=0;i<A*B;i++){
        ans+=!ok[i];
        ok[i+A]|=ok[i];
        ok[i+B]|=ok[i];
        ok[i+C]|=ok[i];
    }
    cout<<ans<<endl;
}