#include <stdio.h>

#define int64 long long

int64 floor(int64 xx, int64 bb)
{
  return (xx / bb);
}

int main()
{
  int64 aa, bb, nn;
  scanf("%lld %lld %lld", &aa, &bb, &nn);
  int64 ans;
  if(bb > nn)
  {
    ans = floor(aa * nn, bb) - aa * floor(nn, bb);
  }
  else if(bb == nn)
  {
    ans = floor(aa * (nn - 1), bb) - aa * floor((nn - 1), bb);
  }
  else
  {
    int64 tmp = nn / bb;
    ans = floor(aa * (tmp * bb - 1), bb) - aa * floor((tmp * bb - 1), bb);
  }
  printf("%lld\n", ans);
  return 0;
}