#include<stdio.h>
#include<math.h>
int main(){

    long int A,B,N;

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

    long int i;
    int a,b,y;
    int ans=0;
    int i_max;
//    if( N < B ) i_max = N;
//    else i_max = B;

    for( i = 1; i <= N; i++ ){
        //a = A*i/B;
        //b = i/B;
        y = floor(A*i/B) - (A * floor(i/B));
        //printf("x=%d y=%d a=%d b=%d\n", i, y, a, b);
        if( y > ans ) ans = y;
        else break;
    }

    printf("%d\n", ans);

    return 0;
}
