#include <stdio.h>

int main(void){
    int a,b,n,lp,lq;
    int max = 0;
    scanf("%d%d%d",&a,&b,&n);
    for(int i =0; i <=n; i++){
        lp = a*i/b;
        lq = i/b;
        int ans = lp - a * lq;
        if(max < ans){
            max = ans;
        }
    }
    printf("%d",max);
    return 0;
}