#include <stdio.h>
#include <string.h>

int main(void){
    long long int A,B,N;
    long long int x;
    long long int ans=-1000000000000000000;
    scanf("%ld %ld %ld", &A, &B, &N);

    for(x=0; x<=N; x++){
        if(ans<((A*x/B)-A*((x/B)))){
            ans = (A*x/B)-A*((x/B));
        }
    }
    printf("%ld",ans);
    return 0;
}