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

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

    x=B-1;
    if(x>N){
        x=N;
    }
    ans = (A*x/B)-A*((x/B));
    printf("%ld",ans);
    return 0;
}