//Generated at 2020-05-02 20:51:46 UTC+8
//Created by Alphagocc
#include<bits/stdc++.h>
#ifdef USE_PBDS
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/priority_queue.hpp>
#endif
using namespace std;
#define FORCE_INLINE __inline__ __attribute__((always_inline))
class IO{static const int bufSize=1<<18;char inBuf[bufSize],outBuf[bufSize];char*ip1=inBuf,*ip2=inBuf;int goodReadBit=0,op1=-1,op2=bufSize-1;
template <typename T>FORCE_INLINE void __RI(T&x){int ch=gc(),neg=1;x=0;for(;!(isdigit(ch)||ch=='-'||ch==EOF);ch=gc());if(ch==EOF){goodReadBit=0;return;}if(ch=='-')neg=-1,ch=gc();for(;isdigit(ch);ch=gc())x=x*10+(ch-48)*neg;}
template <typename T>FORCE_INLINE void __RC(T&x){unsigned char ch;while(isspace(ch=gc()));x=ch;}
FORCE_INLINE void __RS(string&x){char ch;x.clear();for(ch=gc();isspace(ch);ch=gc());if(ch==EOF){goodReadBit=0;return;}for(;!isspace(ch);ch=gc())x.push_back(ch);}
public:
FORCE_INLINE int gc(){return ip1==ip2 &&(ip2 =(ip1=inBuf)+fread(inBuf,1,bufSize,stdin),ip1==ip2)?EOF:*ip1++;}
FORCE_INLINE void R(char&x){__RC(x);}FORCE_INLINE void R(unsigned char&x){__RC(x);}FORCE_INLINE void R(string&x){__RS(x);}
template <typename T1,typename T2>FORCE_INLINE void R(pair<T1,T2>&x){R(x.first),R(x.second);}template<typename T>FORCE_INLINE void R(vector<T>&x){for(auto &i:x)R(i);}
template <typename T,typename...Args>FORCE_INLINE void RA(T*a,int n){for(int i=0;i<n;++i)R(a[i]);}template<typename T,typename...Args>FORCE_INLINE void R(T&x,Args&...args){R(x),R(args...);}
template <typename T,typename...Args>FORCE_INLINE void RA(T*a,int n,Args...args){for(int i=0;i<n;++i)RA(a[i],args...);}template<typename T>FORCE_INLINE void R(T&x){static_assert(is_integral<T>::value,"Unsupported types");if(is_integral<T>::value)__RI(x);}
private:
char space=' ';template <typename T>FORCE_INLINE void __WI(T x){static char buf[64];static int len=-1;if(x>=0){do{buf[++len]=x%10+48,x/=10;}while(x);}else{pc('-');do{buf[++len]=-(x%10)+48,x/=10;}while(x);}while(len>=0){pc(buf[len]),--len;}}
public:
FORCE_INLINE void pc(const char&x){if(op1==op2)flush();outBuf[++op1]=x;}
FORCE_INLINE void flush(){fwrite(outBuf,1,op1+1,stdout),op1=-1;}FORCE_INLINE IO& W(const char&x){pc(x);return(*this);}FORCE_INLINE IO& W(const char*x){while(*x!='\0')pc(*(x++));return(*this);}FORCE_INLINE IO& W(const string&x){W(x.c_str());return(*this);}
template<typename T>FORCE_INLINE IO& W(const vector<T>&x){for(auto &i:x)WS(i);WL();return(*this);}FORCE_INLINE IO& WL(){W('\n');return(*this);}
template<typename T>FORCE_INLINE IO& WL(const T&x){W(x),W('\n');return(*this);}FORCE_INLINE IO& WS(){W(' ');return(*this);}
template<typename T>FORCE_INLINE IO& WS(const T&x){W(x),W(space);return(*this);}
template<typename T>FORCE_INLINE IO& WA(T* a,int n){for(int i=0;i<n;i++)WS(a[i]);WL();return(*this);}
template<typename T,typename...Args>FORCE_INLINE IO& W(const T&x,const Args&...args){W(x),W(space),W(args...);return(*this);}
template<typename...Args>FORCE_INLINE IO& WL(const Args&...args){W(args...),W('\n');return(*this);}
template<typename T,typename...Args>FORCE_INLINE IO& WA(T* a,int n,Args...args){for(int i=0;i<n;i++)WA(a[i],args...);return(*this);}
template<typename T>FORCE_INLINE IO& W(const T&x){static_assert(is_integral<T>::value,"Unsupported types");if(is_integral<T>::value)__WI(x);return(*this);}
template<typename T>FORCE_INLINE IO&operator>>(T&x){R(x);return(*this);}
template<typename T>FORCE_INLINE IO&operator<<(const T&x){W(x);return(*this);}IO(){}}io;
#define REP(i,x,y) for(int i=x;i<y;i++)
#define ALL(x) x.begin(),x.end()
void EXIT(int code){io.flush(),exit(code);}
const int8_t INFC=0x3f;
const int16_t INFS=0x3f3f;
const int32_t INF=0x3f3f3f3f;
const int64_t INFL=0x3f3f3f3f3f3f3f3fLL;

int64_t calc(int64_t a, int64_t b, int64_t x)
{
    return a * x / b - a * (x / b);
}
int main()
{
    int64_t a, b, n;
    io >> a >> b >> n;
    // int64_t ans = 0;
    // for (int i = 1; i <= n; i++) ans = max(ans, calc(a, b, i));
    io.WL(calc(a, b, min(b - 1, n)));
    EXIT(0);
}

Measured memory_bytes: 3648