#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>
#include<limits.h>

#define MAX(a, b) (a>b?a:b)
#define MIN(a, b) (a<b?a:b)
#define MOD 1000000007

int compare(const void* a, const void* b) {
    return *(int*)a-*(int*)b;
}

int findMax(int* a, int n) {
    int i, max = INT_MIN, max_ind = -1;
    for(i=0;i<n;i++) {
        if(a[i] >= max) {
            max = a[i];
            max_ind = i;
        }
    }
    return max_ind;
}

void testCase() {
    long long int i, a, b, n, res;
    if(scanf("%lld%lld%lld", &a, &b, &n)) {
        if(n < b) {
            res = (a*n)/b;
        }
        else {
            res = (a*(b-1))/b;
        }
        printf("%lld\n", res);
    }
}

int main() {
    int t=1;
    // scanf("%d", &t);
    while(t--) {
        testCase();
    }
    return 0;
}