#include <stdio.h>

int main(void){
    long long int a,b,n;
    scanf("%lld %lld %lld",&a,&b,&n);
    if(b>n){
        printf("%lld\n",(a*n)/b-a*(n/b));
    }
    else{
        n--;
        printf("%lld\n",(a*n)/b-a*(n/b));
    }
    return 0;
}