#include <iostream>
using namespace std;
using i64 = long long;

class range {private: struct I{int x;int operator*(){return x;}bool operator!=(I& lhs){return x<lhs.x;}void operator++(){++x;}};I i,n;
public:range(int n):i({0}),n({n}){}range(int i,int n):i({i}),n({n}){}I& begin(){return i;}I& end(){return n;}};

const i64 inf = 987654321987654321;

int main(void) {
  i64 a, b, t; scanf("%lld%lld%lld", &a, &b, &t);
  i64 res = inf;
  for(int y=0; b*y<=t+b && y<=a; y++) {
    i64 x = (t - b*y + a - 1) / a;
    res = min(res, a*x + b*y);
  }
  printf("%lld\n", res);
  return 0;
}

// 最後に一度さよならを 幸せに続くさよならを
// 同じ時を少しばかり生きた証にしよう