#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<cctype>
#include<math.h>
#include<string>
#include<string.h>
#include<stack>
#include<queue>
#include<vector>
#include<utility>
#include<set>
#include<map>
#include<stdlib.h>
#include<iomanip>

using namespace std;

#define ll long long
#define ld long double
#define EPS 0.0000000001
#define INF 1e9
#define MOD 1000000007
#define rep(i,n) for(int i=0;i<(n);i++)
#define loop(i,a,n) for(int i=a;i<(n);i++)
#define all(in) in.begin(),in.end()
#define shosu(x) fixed<<setprecision(x)

#define int ll //!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

typedef vector<int> vi;
typedef vector<string> vs;
typedef pair<int,int> pii;

int gcd(int a, int b){
    if(b==0) return a;
    return gcd(b,a%b);
}
int lcm(int a, int b){
    return a*b/gcd(a,b);
}

typedef vector<vi> vvi;

void printMatrix(vvi a){
    rep(i,a.size()){
        rep(j,a[0].size())cout << a[i][j] << " " ;
        cout << endl;
    }
}

vvi product(vvi a, vvi b, int mod){//ret = a * b % mod
    vvi ret(a.size(), vi(b[0].size(),0));
    rep(i,a.size())rep(j,b[0].size()){
        rep(k,a[0].size()) (ret[i][j] += a[i][k]*b[k][j]) %= mod;
    }
    return ret;
}


vvi powMatrix(vvi a, int t, int mod){// A^t % mod
    int n = a.size();

    vvi ret(n, vi(n,0));
    rep(i,n)ret[i][i] = 1; // 単位行列

    while(t > 0){ //繰り返し自乗法
        if(t&1) ret = product(ret, a, mod);
        a = product(a,a, mod);
        t = t >> 1;
    }
    return ret;
}

signed main(void) {
    int i,j;
    int n,b,c;
    cin >> b >> c >> n;
    b %= MOD;
    c %= MOD;
    vvi a(2,vi(2));
    a[0][0] = c;
    a[0][1] = b;
    a[1][0] = 0;
    a[1][1] = 1;
    vvi t(2,vi(1));
    t[0][0] = b;
    t[1][0] = 1;
    vvi ans = powMatrix(a,n,MOD);
    //printMatrix(ans);
    ans = product(ans,t,MOD);
    //printMatrix(ans);
    cout << (MOD+ans[0][0]-b)%MOD << endl;


}