#include<stdio.h>

int main(void){
    /*int N,M,Q;

    scanf("%d %d %d",&N,&M,&Q);

    int a[Q],b[Q],c[Q],d[Q]; */

    long long int A,B,N,x,n=0,temp1,temp2,temp;

    scanf("%lld %lld %lld",&A,&B,&N);

    for(x=0;x<=N;x++){
        temp1 = A*x/B;
        temp2 = x/B*A;
        temp = temp1 - temp2;
        if(temp>n) n = temp;
    }

    printf("%lld",n);

    return 0;
}