#include <stdio.h>

int myfloor(double t){
    return (int)t;
}


int main(void){
    int a, b, n, e, f = -1000;
    scanf("%d %d %d", &a, &b, &n);
    for(int x = 1; x <= n; x++){
        e = myfloor(a*x/b) - a*myfloor(x/b);
        if(f < e){
            f = e;
        }
    }
    printf("%d", f);
    return 0;
}
