#include<bits/stdc++.h>
using lint=long long;
int main(){
    std::cin.tie(nullptr);std::ios_base::sync_with_stdio(false);
    std::cout.setf(std::ios_base::fixed);std::cout.precision(15);
    lint a,b,c;std::cin>>a>>b>>c;
    lint num=std::abs(c-b),den=std::abs(b-a);
    if((a<b)^(b<c))num=-num;
    lint d=b-a*num/den;
    std::cout<<c*num/den+d<<'\n';
}