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

long a, b, n;

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

    long x, ans;
    if (n>=b){
        x = b-1;
    }
    else{
        x = n;
    }
    
    ans = floor(a*x/b) - a*floor(x/b);
    printf("%ld\n", ans);

    return 0;
}
