#include <stdio.h>
#include <math.h>

int main(){
    long int a,b,n;
    long int t,u;
    long int x,m = 0;

    scanf("%ld %ld %ld", &a, &b, &n);

    for(int i = 1; i <= n; i++){
        t = a * i / b;
        u = i / b;
        x = t - a * u;
    
        if(x >= 0 && x >= m){
            m = x;
        }
        if(i == n) break;
    }
    
    //printf("loop end");
    printf("%ld", m);

}