#include<stdio.h>

int main(){
    long long int N,A,B;
    long long int i, tmp = 0, tmp2;
    scanf("%lld %lld %lld", &A, &B, &N);

    i = N;
    tmp2 = A * i / B - (A * (i / B));
    //printf("%lld %lld\n", A * i / B, (A * (i / B)));
    if (tmp < tmp2)
        tmp = tmp2;

    for (i = B - 1; i <= N; i+=B){
        tmp2 = A * i / B - (A * (i / B));
        //printf("%lld %lld\n", A * i / B, (A * (i / B)));
        if (tmp < tmp2)
            tmp = tmp2;
        else
            break;
    }
    printf("%lld\n", tmp);
    return 0;
}